from __future__ import annotations

import contextlib
import operator
import sys
import warnings
from datetime import datetime
from functools import partial

import numpy as np
import pandas as pd
import pytest

import dask
import dask.dataframe as dd
from dask._compatibility import WINDOWS
from dask.dataframe import _compat
from dask.dataframe._compat import (
    PANDAS_GE_210,
    PANDAS_GE_220,
    PANDAS_GE_230,
    PANDAS_GE_300,
    check_observed_deprecation,
    tm,
)
from dask.dataframe._pyarrow import to_pyarrow_string
from dask.dataframe.backends import grouper_dispatch
from dask.dataframe.groupby import NUMERIC_ONLY_NOT_IMPLEMENTED
from dask.dataframe.utils import assert_eq, pyarrow_strings_enabled
from dask.utils import M

if PANDAS_GE_220 and not PANDAS_GE_300:
    pytestmark = [
        pytest.mark.filterwarnings(
            r"ignore:.*DataFrameGroupBy\.apply:DeprecationWarning"
        ),
        pytest.mark.filterwarnings(r"ignore:.*DataFrameGroupBy\.apply:FutureWarning"),
    ]


AGG_FUNCS = [
    "sum",
    "mean",
    "median",
    "min",
    "max",
    "count",
    "size",
    "std",
    "var",
    "cov",
    "corr",
    "nunique",
    "first",
    "last",
    "prod",
]

INCLUDE_GROUPS = {"include_groups": False} if PANDAS_GE_220 else {}


@pytest.fixture(params=AGG_FUNCS)
def agg_func(request):
    """
    Aggregations supported for groups
    """
    return request.param


# Wrapper fixture for shuffle_method to auto-apply it to all the tests in this module,
# as we don't want to auto-apply the fixture repo-wide.
@pytest.fixture(autouse=True)
def auto_shuffle_method(shuffle_method):
    yield


@contextlib.contextmanager
def groupby_axis_deprecated(*contexts, dask_op=True):
    with contextlib.ExitStack() as stack:
        for ctx in contexts:
            stack.enter_context(ctx)
        if PANDAS_GE_210 and not dask_op:
            stack.enter_context(pytest.warns(FutureWarning, match="axis"))
        yield


@pytest.mark.xfail(reason="uncertain how to handle. See issue #3481.")
def test_groupby_internal_repr_xfail():
    pdf = pd.DataFrame({"x": [0, 1, 2, 3, 4, 6, 7, 8, 9, 10], "y": list("abcbabbcda")})
    ddf = dd.from_pandas(pdf, 3)

    gp = pdf.groupby("y")["x"]
    dp = ddf.groupby("y")["x"]
    assert isinstance(dp.obj, dd.Series)
    assert_eq(dp.obj, gp.obj)

    gp = pdf.groupby(pdf.y)["x"]
    dp = ddf.groupby(ddf.y)["x"]
    assert isinstance(dp.obj, dd.Series)


def test_groupby_error():
    pdf = pd.DataFrame({"x": [0, 1, 2, 3, 4, 6, 7, 8, 9, 10], "y": list("abcbabbcda")})
    ddf = dd.from_pandas(pdf, 3)

    with pytest.raises(KeyError):
        ddf.groupby("A")

    with pytest.raises(KeyError):
        ddf.groupby(["x", "A"])

    dp = ddf.groupby("y")

    msg = "Column not found: "
    with pytest.raises(KeyError) as err:
        dp["A"]
    assert msg in str(err.value)

    msg = "Columns not found: "
    with pytest.raises(KeyError) as err:
        dp[["x", "A"]]
    assert msg in str(err.value)

    msg = (
        "DataFrameGroupBy does not allow compute method."
        "Please chain it with an aggregation method (like ``.mean()``) or get a "
        "specific group using ``.get_group()`` before calling ``compute()``"
    )

    with pytest.raises(NotImplementedError) as err:
        dp.compute()
    assert msg in str(err.value)


def test_full_groupby():
    df = pd.DataFrame(
        {"a": [1, 2, 3, 4, 5, 6, 7, 8, 9], "b": [4, 5, 6, 3, 2, 1, 0, 0, 0]},
        index=[0, 1, 3, 5, 6, 8, 9, 9, 9],
    )
    ddf = dd.from_pandas(df, npartitions=3)

    pytest.raises(KeyError, lambda: ddf.groupby("does_not_exist"))
    pytest.raises(AttributeError, lambda: ddf.groupby("a").does_not_exist)
    assert "b" in dir(ddf.groupby("a"))

    def func(df):
        return df.assign(b=df.b - df.b.mean())

    expected = df.groupby("a").apply(func, **INCLUDE_GROUPS)

    with pytest.warns(UserWarning, match="`meta` is not specified"):
        assert_eq(expected, ddf.groupby("a").apply(func, **INCLUDE_GROUPS))


@pytest.mark.parametrize(
    "grouper",
    [
        lambda df: ["a"],
        lambda df: ["a", "b"],
        lambda df: df["a"],
        lambda df: [df["a"], df["b"]],
        lambda df: [df["a"] > 2, df["b"] > 1],
    ],
)
@pytest.mark.parametrize("reverse", [True, False])
def test_full_groupby_multilevel(grouper, reverse):
    index = [0, 1, 3, 5, 6, 8, 9, 9, 9]
    if reverse:
        index.reverse()
    df = pd.DataFrame(
        {
            "a": [1, 2, 3, 4, 5, 6, 7, 8, 9],
            "d": [1, 2, 3, 4, 5, 6, 7, 8, 9],
            "b": [4, 5, 6, 3, 2, 1, 0, 0, 0],
        },
        index=index,
    )
    ddf = dd.from_pandas(df, npartitions=3)

    def func(df):
        return df.assign(b=df.d - df.d.mean())

    with pytest.warns(UserWarning, match="`meta` is not specified"):
        assert_eq(
            df.groupby(grouper(df)).apply(func, **INCLUDE_GROUPS),
            ddf.groupby(grouper(ddf)).apply(func, **INCLUDE_GROUPS),
        )


def test_groupby_dir():
    df = pd.DataFrame({"a": range(10), "b c d e": range(10)})
    ddf = dd.from_pandas(df, npartitions=2)
    g = ddf.groupby("a")
    assert "a" in dir(g)
    assert "b c d e" not in dir(g)


@pytest.mark.parametrize("scheduler", ["sync", "threads"])
def test_groupby_on_index(scheduler):
    pdf = pd.DataFrame(
        {"a": [1, 2, 3, 4, 5, 6, 7, 8, 9], "b": [4, 5, 6, 3, 2, 1, 0, 0, 0]},
        index=[0, 1, 3, 5, 6, 8, 9, 9, 9],
    )
    ddf = dd.from_pandas(pdf, npartitions=3)

    ddf2 = ddf.set_index("a")
    pdf2 = pdf.set_index("a")
    assert_eq(ddf.groupby("a").b.mean(), ddf2.groupby(ddf2.index).b.mean())

    # Check column projection for `groupby().agg`
    agg = ddf2.groupby("a").agg({"b": "mean"})
    assert_eq(ddf.groupby("a").b.mean(), agg.b)

    def func(df):
        return df.assign(b=df.b - df.b.mean())

    def func2(df):
        return df[["b"]] - df[["b"]].mean()

    def func3(df):
        return df.mean()

    with dask.config.set(scheduler=scheduler):
        with warnings.catch_warnings():
            warnings.simplefilter("ignore", UserWarning)
            assert_eq(
                ddf.groupby("a").apply(func, **INCLUDE_GROUPS),
                pdf.groupby("a").apply(func, **INCLUDE_GROUPS),
            )

            assert_eq(
                pdf2.groupby(pdf2.index).apply(func2, **INCLUDE_GROUPS),
                ddf2.groupby(ddf2.index).apply(func2, **INCLUDE_GROUPS),
            )

            assert_eq(
                ddf2.b.groupby("a").apply(func3, **INCLUDE_GROUPS),
                pdf2.b.groupby("a").apply(func3, **INCLUDE_GROUPS),
            )

            assert_eq(
                ddf2.b.groupby(ddf2.index).apply(func3, **INCLUDE_GROUPS),
                pdf2.b.groupby(pdf2.index).apply(func3, **INCLUDE_GROUPS),
            )


@pytest.mark.filterwarnings("ignore:invalid value encountered:RuntimeWarning")
@pytest.mark.parametrize(
    "grouper_id,grouper",
    [
        (0, lambda df: df.groupby("a")["b"]),
        (1, lambda df: df.groupby(["a", "b"])),
        (2, lambda df: df.groupby(["a", "b"])["c"]),
        (3, lambda df: df.groupby(df["a"])[["b", "c"]]),
        (4, lambda df: df.groupby("a")[["b", "c"]]),
        (5, lambda df: df.groupby("a")[["b"]]),
        (6, lambda df: df.groupby(["a", "b", "c"])),
    ],
)
def test_groupby_multilevel_getitem(xfail, grouper_id, grouper, agg_func):
    # nunique is not implemented for DataFrameGroupBy
    if agg_func == "nunique" and grouper_id in (1, 3, 4, 5, 6):
        xfail("not implemented for DataFrameGroupBy")

    df = pd.DataFrame(
        {
            "a": [1, 2, 3, 1, 2, 3],
            "b": [1, 2, 1, 4, 2, 1],
            "c": [1, 3, 2, 1, 1, 2],
            "d": [1, 2, 1, 1, 2, 2],
        }
    )
    ddf = dd.from_pandas(df, 2)

    dask_group = grouper(ddf)
    pandas_group = grouper(df)

    # covariance/correlation only works with N+1 columns
    if isinstance(pandas_group, pd.core.groupby.SeriesGroupBy) and agg_func in (
        "cov",
        "corr",
    ):
        return

    dask_agg = getattr(dask_group, agg_func)
    pandas_agg = getattr(pandas_group, agg_func)
    assert isinstance(pandas_group, pd.core.groupby.GroupBy)

    if agg_func == "mean":
        assert_eq(dask_agg(), pandas_agg().astype(float))
    else:
        a = dask_agg()
        with warnings.catch_warnings():
            # pandas does `.cov([[1], [1]])` which numpy warns on (all NaN).
            # Pandas does strange things with exceptions in groupby.
            warnings.simplefilter("ignore", RuntimeWarning)
            b = pandas_agg()
        assert_eq(a, b)


def test_groupby_multilevel_agg():
    df = pd.DataFrame(
        {
            "a": [1, 2, 3, 1, 2, 3],
            "b": [1, 2, 1, 4, 2, 1],
            "c": [1, 3, 2, 1, 1, 2],
            "d": [1, 2, 1, 1, 2, 2],
        }
    )
    ddf = dd.from_pandas(df, 2)

    sol = df.groupby(["a"]).mean()
    res = ddf.groupby(["a"]).mean()
    assert_eq(res, sol)

    sol = df.groupby(["a", "c"]).mean()
    res = ddf.groupby(["a", "c"]).mean()
    assert_eq(res, sol)

    sol = df.groupby([df["a"], df["c"]]).mean()
    res = ddf.groupby([ddf["a"], ddf["c"]]).mean()
    assert_eq(res, sol)


@pytest.mark.parametrize(
    "categoricals,by",
    [
        (True, lambda df: "b"),
        (False, lambda df: "b"),
        (True, lambda df: df.b),
        (False, lambda df: df.b),
        (False, lambda df: df.b + 1),
    ],
)
def test_groupby_get_group(categoricals, by):
    dsk = {
        ("x", 0): pd.DataFrame({"a": [1, 2, 6], "b": [4, 2, 7]}, index=[0, 1, 3]),
        ("x", 1): pd.DataFrame({"a": [4, 2, 6], "b": [3, 3, 1]}, index=[5, 6, 8]),
        ("x", 2): pd.DataFrame({"a": [4, 3, 7], "b": [1, 1, 3]}, index=[9, 9, 9]),
    }
    ddf = dd.repartition(pd.concat(dsk.values()), divisions=[0, 4, 9, 9])

    if categoricals:
        ddf = ddf.categorize(columns=["b"])
    pdf = ddf.compute()

    if PANDAS_GE_210 and categoricals and not PANDAS_GE_300:
        ctx = pytest.warns(FutureWarning, match="The default of observed=False")
    else:
        ctx = contextlib.nullcontext()

    with ctx:
        ddgrouped = ddf.groupby(by(ddf))
    with ctx:
        pdgrouped = pdf.groupby(by(pdf))

    # DataFrame
    assert_eq(ddgrouped.get_group(2), pdgrouped.get_group(2))
    assert_eq(ddgrouped.get_group(3), pdgrouped.get_group(3))
    # Series
    assert_eq(ddgrouped.a.get_group(3), pdgrouped.a.get_group(3))
    assert_eq(ddgrouped.a.get_group(2), pdgrouped.a.get_group(2))


def test_dataframe_groupby_nunique():
    strings = list("aaabbccccdddeee")
    data = np.random.randn(len(strings))
    ps = pd.DataFrame(dict(strings=strings, data=data))
    s = dd.from_pandas(ps, npartitions=3)
    expected = ps.groupby("strings")["data"].nunique()
    result = s.groupby("strings")["data"].nunique()
    assert_eq(result, expected)


def test_dataframe_groupby_nunique_across_group_same_value():
    strings = list("aaabbccccdddeee")
    data = list(map(int, "123111223323412"))
    ps = pd.DataFrame(dict(strings=strings, data=data))
    s = dd.from_pandas(ps, npartitions=3)
    expected = ps.groupby("strings")["data"].nunique()
    result = s.groupby("strings")["data"].nunique()
    assert_eq(result, expected)


def test_series_groupby_propagates_names():
    df = pd.DataFrame({"x": [1, 2, 3], "y": [4, 5, 6]})
    ddf = dd.from_pandas(df, 2)
    func = lambda df: df["y"].sum()
    with pytest.warns(UserWarning):  # meta inference
        result = ddf.groupby("x").apply(func, **INCLUDE_GROUPS)
    expected = df.groupby("x").apply(func, **INCLUDE_GROUPS)
    assert_eq(result, expected)


@pytest.mark.parametrize("npartitions", (1, 2))
@pytest.mark.parametrize("func", ("cumsum", "cumprod", "cumcount"))
def test_series_groupby_cumfunc_with_named_index(npartitions, func):
    df = pd.DataFrame(
        {"x": [1, 2, 3, 4, 5, 6, 7], "y": [8, 9, 6, 2, 3, 5, 6]}
    ).set_index("x")
    ddf = dd.from_pandas(df, npartitions)
    assert ddf.npartitions == npartitions
    expected = getattr(df["y"].groupby("x"), func)()
    result = getattr(ddf["y"].groupby("x"), func)()
    assert_eq(result, expected)


def test_series_groupby():
    s = pd.Series([1, 2, 2, 1, 1])
    pd_group = s.groupby(s)

    ss = dd.from_pandas(s, npartitions=2)
    dask_group = ss.groupby(ss)

    pd_group2 = s.groupby(s + 1)
    dask_group2 = ss.groupby(ss + 1)

    for dg, pdg in [(dask_group, pd_group), (pd_group2, dask_group2)]:
        assert_eq(dg.count(), pdg.count())
        assert_eq(dg.sum(), pdg.sum())
        assert_eq(dg.min(), pdg.min())
        assert_eq(dg.max(), pdg.max())
        assert_eq(dg.size(), pdg.size())
        assert_eq(dg.first(), pdg.first())
        assert_eq(dg.last(), pdg.last())
        assert_eq(dg.prod(), pdg.prod())


def test_series_groupby_errors():
    s = pd.Series([1, 2, 2, 1, 1])

    ss = dd.from_pandas(s, npartitions=2)

    msg = "No group keys passed!"
    with pytest.raises(ValueError) as err:
        s.groupby([])  # pandas
    assert msg in str(err.value)
    with pytest.raises(ValueError) as err:
        ss.groupby([])  # dask should raise the same error
    assert msg in str(err.value)

    sss = dd.from_pandas(s, npartitions=5)
    with pytest.raises((NotImplementedError, ValueError)):
        ss.groupby(sss)

    with pytest.raises(KeyError):
        s.groupby("x")  # pandas
    with pytest.raises(KeyError):
        ss.groupby("x")  # dask should raise the same error


def test_groupby_index_array():
    df = _compat.makeTimeDataFrame()
    ddf = dd.from_pandas(df, npartitions=2)

    # first select column, then group
    assert_eq(
        df.A.groupby(df.index.month).nunique(),
        ddf.A.groupby(ddf.index.month).nunique(),
        check_names=False,
    )

    # first group, then select column
    assert_eq(
        df.groupby(df.index.month).A.nunique(),
        ddf.groupby(ddf.index.month).A.nunique(),
        check_names=False,
    )


def test_groupby_set_index():
    df = _compat.makeTimeDataFrame()
    ddf = dd.from_pandas(df, npartitions=2)
    pytest.raises(TypeError, lambda: ddf.groupby(df.index.month, as_index=False))


@pytest.mark.parametrize("empty", [True, False])
def test_split_apply_combine_on_series(empty):
    if empty:
        pdf = pd.DataFrame({"a": [1.0], "b": [1.0]}, index=[0]).iloc[:0]
        # There's a bug in pandas where df.groupby(...).var(ddof=0) results in
        # no columns. Just skip these checks for now.
        ddofs = []
    else:
        ddofs = [0, 1, 2]
        pdf = pd.DataFrame(
            {"a": [1, 2, 6, 4, 4, 6, 4, 3, 7], "b": [4, 2, 7, 3, 3, 1, 1, 1, 2]},
            index=[0, 1, 3, 5, 6, 8, 9, 9, 9],
        )
    ddf = dd.from_pandas(pdf, npartitions=3)

    for ddkey, pdkey in [("b", "b"), (ddf.b, pdf.b), (ddf.b + 1, pdf.b + 1)]:
        assert_eq(ddf.groupby(ddkey).a.min(), pdf.groupby(pdkey).a.min())
        assert_eq(ddf.groupby(ddkey).a.max(), pdf.groupby(pdkey).a.max())
        assert_eq(ddf.groupby(ddkey).a.count(), pdf.groupby(pdkey).a.count())
        assert_eq(ddf.groupby(ddkey).a.mean(), pdf.groupby(pdkey).a.mean())
        assert_eq(ddf.groupby(ddkey).a.nunique(), pdf.groupby(pdkey).a.nunique())
        assert_eq(ddf.groupby(ddkey).a.size(), pdf.groupby(pdkey).a.size())
        assert_eq(ddf.groupby(ddkey).a.first(), pdf.groupby(pdkey).a.first())
        assert_eq(ddf.groupby(ddkey).a.last(), pdf.groupby(pdkey).a.last())
        assert_eq(ddf.groupby(ddkey).a.tail(), pdf.groupby(pdkey).a.tail())
        assert_eq(ddf.groupby(ddkey).a.head(), pdf.groupby(pdkey).a.head())
        for ddof in ddofs:
            assert_eq(ddf.groupby(ddkey).a.var(ddof), pdf.groupby(pdkey).a.var(ddof))
            assert_eq(ddf.groupby(ddkey).a.std(ddof), pdf.groupby(pdkey).a.std(ddof))

        assert_eq(ddf.groupby(ddkey).sum(), pdf.groupby(pdkey).sum())
        assert_eq(ddf.groupby(ddkey).min(), pdf.groupby(pdkey).min())
        assert_eq(ddf.groupby(ddkey).max(), pdf.groupby(pdkey).max())
        assert_eq(ddf.groupby(ddkey).count(), pdf.groupby(pdkey).count())
        assert_eq(ddf.groupby(ddkey).mean(), pdf.groupby(pdkey).mean())
        assert_eq(ddf.groupby(ddkey).size(), pdf.groupby(pdkey).size())
        assert_eq(ddf.groupby(ddkey).first(), pdf.groupby(pdkey).first())
        assert_eq(ddf.groupby(ddkey).last(), pdf.groupby(pdkey).last())
        assert_eq(ddf.groupby(ddkey).prod(), pdf.groupby(pdkey).prod())

        for ddof in ddofs:
            assert_eq(
                ddf.groupby(ddkey).var(ddof),
                pdf.groupby(pdkey).var(ddof),
                check_dtype=False,
            )
            assert_eq(
                ddf.groupby(ddkey).std(ddof),
                pdf.groupby(pdkey).std(ddof),
                check_dtype=False,
            )

    for ddkey, pdkey in [(ddf.b, pdf.b), (ddf.b + 1, pdf.b + 1)]:
        assert_eq(
            ddf.a.groupby(ddkey).sum(), pdf.a.groupby(pdkey).sum(), check_names=False
        )
        assert_eq(
            ddf.a.groupby(ddkey).max(), pdf.a.groupby(pdkey).max(), check_names=False
        )
        assert_eq(
            ddf.a.groupby(ddkey).count(),
            pdf.a.groupby(pdkey).count(),
            check_names=False,
        )
        assert_eq(
            ddf.a.groupby(ddkey).mean(), pdf.a.groupby(pdkey).mean(), check_names=False
        )
        assert_eq(
            ddf.a.groupby(ddkey).nunique(),
            pdf.a.groupby(pdkey).nunique(),
            check_names=False,
        )
        assert_eq(
            ddf.a.groupby(ddkey).first(),
            pdf.a.groupby(pdkey).first(),
            check_names=False,
        )
        assert_eq(
            ddf.a.groupby(ddkey).last(), pdf.a.groupby(pdkey).last(), check_names=False
        )
        assert_eq(
            ddf.a.groupby(ddkey).prod(), pdf.a.groupby(pdkey).prod(), check_names=False
        )

        for ddof in ddofs:
            assert_eq(ddf.a.groupby(ddkey).var(ddof), pdf.a.groupby(pdkey).var(ddof))
            assert_eq(ddf.a.groupby(ddkey).std(ddof), pdf.a.groupby(pdkey).std(ddof))

    for i in [0, 4, 7]:
        assert_eq(ddf.groupby(ddf.b > i).a.sum(), pdf.groupby(pdf.b > i).a.sum())
        assert_eq(ddf.groupby(ddf.b > i).a.min(), pdf.groupby(pdf.b > i).a.min())
        assert_eq(ddf.groupby(ddf.b > i).a.max(), pdf.groupby(pdf.b > i).a.max())
        assert_eq(ddf.groupby(ddf.b > i).a.count(), pdf.groupby(pdf.b > i).a.count())
        assert_eq(ddf.groupby(ddf.b > i).a.mean(), pdf.groupby(pdf.b > i).a.mean())
        assert_eq(
            ddf.groupby(ddf.b > i).a.nunique(), pdf.groupby(pdf.b > i).a.nunique()
        )
        assert_eq(ddf.groupby(ddf.b > i).a.size(), pdf.groupby(pdf.b > i).a.size())
        assert_eq(ddf.groupby(ddf.b > i).a.first(), pdf.groupby(pdf.b > i).a.first())
        assert_eq(ddf.groupby(ddf.b > i).a.last(), pdf.groupby(pdf.b > i).a.last())
        assert_eq(ddf.groupby(ddf.b > i).a.tail(), pdf.groupby(pdf.b > i).a.tail())
        assert_eq(ddf.groupby(ddf.b > i).a.head(), pdf.groupby(pdf.b > i).a.head())
        assert_eq(ddf.groupby(ddf.b > i).a.prod(), pdf.groupby(pdf.b > i).a.prod())

        assert_eq(ddf.groupby(ddf.a > i).b.sum(), pdf.groupby(pdf.a > i).b.sum())
        assert_eq(ddf.groupby(ddf.a > i).b.min(), pdf.groupby(pdf.a > i).b.min())
        assert_eq(ddf.groupby(ddf.a > i).b.max(), pdf.groupby(pdf.a > i).b.max())
        assert_eq(ddf.groupby(ddf.a > i).b.count(), pdf.groupby(pdf.a > i).b.count())
        assert_eq(ddf.groupby(ddf.a > i).b.mean(), pdf.groupby(pdf.a > i).b.mean())
        assert_eq(
            ddf.groupby(ddf.a > i).b.nunique(), pdf.groupby(pdf.a > i).b.nunique()
        )
        assert_eq(ddf.groupby(ddf.b > i).b.size(), pdf.groupby(pdf.b > i).b.size())
        assert_eq(ddf.groupby(ddf.b > i).b.first(), pdf.groupby(pdf.b > i).b.first())
        assert_eq(ddf.groupby(ddf.b > i).b.last(), pdf.groupby(pdf.b > i).b.last())
        assert_eq(ddf.groupby(ddf.b > i).b.tail(), pdf.groupby(pdf.b > i).b.tail())
        assert_eq(ddf.groupby(ddf.b > i).b.head(), pdf.groupby(pdf.b > i).b.head())
        assert_eq(ddf.groupby(ddf.b > i).b.prod(), pdf.groupby(pdf.b > i).b.prod())

        assert_eq(ddf.groupby(ddf.b > i).sum(), pdf.groupby(pdf.b > i).sum())
        assert_eq(ddf.groupby(ddf.b > i).min(), pdf.groupby(pdf.b > i).min())
        assert_eq(ddf.groupby(ddf.b > i).max(), pdf.groupby(pdf.b > i).max())
        assert_eq(ddf.groupby(ddf.b > i).count(), pdf.groupby(pdf.b > i).count())
        assert_eq(ddf.groupby(ddf.b > i).mean(), pdf.groupby(pdf.b > i).mean())
        assert_eq(ddf.groupby(ddf.b > i).size(), pdf.groupby(pdf.b > i).size())
        assert_eq(ddf.groupby(ddf.b > i).first(), pdf.groupby(pdf.b > i).first())
        assert_eq(ddf.groupby(ddf.b > i).last(), pdf.groupby(pdf.b > i).last())
        assert_eq(ddf.groupby(ddf.b > i).prod(), pdf.groupby(pdf.b > i).prod())

        assert_eq(ddf.groupby(ddf.a > i).sum(), pdf.groupby(pdf.a > i).sum())
        assert_eq(ddf.groupby(ddf.a > i).min(), pdf.groupby(pdf.a > i).min())
        assert_eq(ddf.groupby(ddf.a > i).max(), pdf.groupby(pdf.a > i).max())
        assert_eq(ddf.groupby(ddf.a > i).count(), pdf.groupby(pdf.a > i).count())
        assert_eq(ddf.groupby(ddf.a > i).mean(), pdf.groupby(pdf.a > i).mean())
        assert_eq(ddf.groupby(ddf.a > i).size(), pdf.groupby(pdf.a > i).size())
        assert_eq(ddf.groupby(ddf.a > i).first(), pdf.groupby(pdf.a > i).first())
        assert_eq(ddf.groupby(ddf.a > i).last(), pdf.groupby(pdf.a > i).last())
        assert_eq(ddf.groupby(ddf.a > i).prod(), pdf.groupby(pdf.a > i).prod())

        for ddof in ddofs:
            assert_eq(
                ddf.groupby(ddf.b > i).std(ddof), pdf.groupby(pdf.b > i).std(ddof)
            )

    for ddkey, pdkey in [
        ("a", "a"),
        (ddf.a, pdf.a),
        (ddf.a + 1, pdf.a + 1),
        (ddf.a > 3, pdf.a > 3),
    ]:
        assert_eq(ddf.groupby(ddkey).b.sum(), pdf.groupby(pdkey).b.sum())
        assert_eq(ddf.groupby(ddkey).b.min(), pdf.groupby(pdkey).b.min())
        assert_eq(ddf.groupby(ddkey).b.max(), pdf.groupby(pdkey).b.max())
        assert_eq(ddf.groupby(ddkey).b.count(), pdf.groupby(pdkey).b.count())
        assert_eq(ddf.groupby(ddkey).b.mean(), pdf.groupby(pdkey).b.mean())
        assert_eq(ddf.groupby(ddkey).b.nunique(), pdf.groupby(pdkey).b.nunique())
        assert_eq(ddf.groupby(ddkey).b.size(), pdf.groupby(pdkey).b.size())
        assert_eq(ddf.groupby(ddkey).b.first(), pdf.groupby(pdkey).b.first())
        assert_eq(ddf.groupby(ddkey).last(), pdf.groupby(pdkey).last())
        assert_eq(ddf.groupby(ddkey).prod(), pdf.groupby(pdkey).prod())

        assert_eq(ddf.groupby(ddkey).sum(), pdf.groupby(pdkey).sum())
        assert_eq(ddf.groupby(ddkey).min(), pdf.groupby(pdkey).min())
        assert_eq(ddf.groupby(ddkey).max(), pdf.groupby(pdkey).max())
        assert_eq(ddf.groupby(ddkey).count(), pdf.groupby(pdkey).count())
        assert_eq(ddf.groupby(ddkey).mean(), pdf.groupby(pdkey).mean().astype(float))
        assert_eq(ddf.groupby(ddkey).size(), pdf.groupby(pdkey).size())
        assert_eq(ddf.groupby(ddkey).first(), pdf.groupby(pdkey).first())
        assert_eq(ddf.groupby(ddkey).last(), pdf.groupby(pdkey).last())
        assert_eq(ddf.groupby(ddkey).prod(), pdf.groupby(pdkey).prod())

        for ddof in ddofs:
            assert_eq(ddf.groupby(ddkey).b.std(ddof), pdf.groupby(pdkey).b.std(ddof))

    assert sorted(ddf.groupby("b").a.sum().dask) == sorted(
        ddf.groupby("b").a.sum().dask
    )
    assert sorted(ddf.groupby(ddf.a > 3).b.mean().dask) == sorted(
        ddf.groupby(ddf.a > 3).b.mean().dask
    )

    # test raises with incorrect key
    pytest.raises(KeyError, lambda: ddf.groupby("x"))
    pytest.raises(KeyError, lambda: ddf.groupby(["a", "x"]))
    pytest.raises(KeyError, lambda: ddf.groupby("a")["x"])
    pytest.raises(KeyError, lambda: ddf.groupby("a")["b", "x"])
    pytest.raises(KeyError, lambda: ddf.groupby("a")[["b", "x"]])


@pytest.mark.parametrize("keyword", ["split_every", "split_out"])
def test_groupby_reduction_split(xfail, keyword, agg_func, shuffle_method):
    if (
        agg_func in {"first", "last"}
        and shuffle_method == "disk"
        and keyword == "split_out"
    ):
        xfail(reason="https://github.com/dask/dask/issues/10034")

    pdf = pd.DataFrame(
        {"a": [1, 2, 6, 4, 4, 6, 4, 3, 7] * 100, "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 100}
    )
    ddf = dd.from_pandas(pdf, npartitions=15)

    def call(g, m, **kwargs):
        return getattr(g, m)(**kwargs)

    # DataFrame
    # nunique is not implemented for DataFrameGroupBy
    # covariance/correlation is not a series aggregation
    if agg_func not in ("nunique", "cov", "corr"):
        res = call(ddf.groupby("b", sort=False), agg_func, **{keyword: 2})
        sol = call(pdf.groupby("b"), agg_func)
        assert_eq(res, sol)
        assert call(ddf.groupby("b"), agg_func)._name != res._name

    if agg_func == "var":
        res = call(ddf.groupby("b", sort=False), "var", ddof=2, **{keyword: 2})
        sol = call(pdf.groupby("b"), "var", ddof=2)
        assert_eq(res, sol)
        assert call(ddf.groupby("b"), "var", ddof=2)._name != res._name

    # Series, post select
    # covariance/correlation is not a series aggregation
    if agg_func not in ("cov", "corr"):
        res = call(ddf.groupby("b", sort=False).a, agg_func, **{keyword: 2})
        sol = call(pdf.groupby("b").a, agg_func)
        assert_eq(res, sol)
        assert call(ddf.groupby("b").a, agg_func)._name != res._name

    if agg_func == "var":
        res = call(ddf.groupby("b", sort=False).a, "var", ddof=2, **{keyword: 2})
        sol = call(pdf.groupby("b").a, "var", ddof=2)
        assert_eq(res, sol)
        assert call(ddf.groupby("b").a, "var", ddof=2)._name != res._name

    # Series, pre select
    # covariance/correlation is not a series aggregation
    if agg_func not in ("cov", "corr"):
        res = call(ddf.a.groupby(ddf.b, sort=False), agg_func, **{keyword: 2})
        sol = call(pdf.a.groupby(pdf.b), agg_func)
        # There's a bug in pandas 0.18.0 with `pdf.a.groupby(pdf.b).count()`
        # not forwarding the series name. Skip name checks here for now.
        assert_eq(res, sol, check_names=False)
        assert call(ddf.a.groupby(ddf.b), agg_func)._name != res._name

    if agg_func == "var":
        res = call(ddf.a.groupby(ddf.b, sort=False), "var", ddof=2, **{keyword: 2})
        sol = call(pdf.a.groupby(pdf.b), "var", ddof=2)

        assert_eq(res, sol)
        assert call(ddf.a.groupby(ddf.b), "var", ddof=2)._name != res._name


@pytest.mark.parametrize(
    "grouped",
    [
        lambda df: df.groupby("A"),
        lambda df: df.groupby(df["A"]),
        lambda df: df.groupby(df["A"] + 1),
        lambda df: df.groupby("A")["B"],
        # SeriesGroupBy:
        lambda df: df.groupby("A")["B"],
        lambda df: df.groupby(df["A"])["B"],
        lambda df: df.groupby(df["A"] + 1)["B"],
        # Series.groupby():
        lambda df: df.B.groupby(df["A"]),
        lambda df: df.B.groupby(df["A"] + 1),
        # DataFrameGroupBy with column slice:
        lambda df: df.groupby("A")[["B", "C"]],
        lambda df: df.groupby(df["A"])[["B", "C"]],
        lambda df: df.groupby(df["A"] + 1)[["B", "C"]],
    ],
)
@pytest.mark.parametrize(
    "func",
    [
        lambda grp: grp.apply(lambda x: x.sum(), **INCLUDE_GROUPS),
        lambda grp: grp.transform(lambda x: x.sum()),
    ],
)
def test_apply_or_transform_shuffle(grouped, func):
    pdf = pd.DataFrame(
        {
            "A": [1, 2, 3, 4] * 5,
            "B": np.random.randn(20),
            "C": np.random.randn(20),
            "D": np.random.randn(20),
        }
    )
    ddf = dd.from_pandas(pdf, 3)

    with pytest.warns(UserWarning):  # meta inference
        assert_eq(func(grouped(pdf)), func(grouped(ddf)))


@pytest.mark.parametrize(
    "grouper",
    [
        lambda df: "AA",
        lambda df: ["AA", "AB"],
        lambda df: df["AA"],
        lambda df: [df["AA"], df["AB"]],
        lambda df: df["AA"] + 1,
        lambda df: [df["AA"] + 1, df["AB"] + 1],
    ],
)
@pytest.mark.parametrize(
    "func",
    [
        lambda grouped: grouped.apply(lambda x: x.sum(), **INCLUDE_GROUPS),
        lambda grouped: grouped.transform(lambda x: x.sum()),
    ],
)
def test_apply_or_transform_shuffle_multilevel(grouper, func):
    pdf = pd.DataFrame(
        {
            "AB": [1, 2, 3, 4] * 5,
            "AA": [1, 2, 3, 4] * 5,
            "B": np.random.randn(20),
            "C": np.random.randn(20),
            "D": np.random.randn(20),
        }
    )
    ddf = dd.from_pandas(pdf, 3)

    with pytest.warns(UserWarning):
        # DataFrameGroupBy
        assert_eq(func(ddf.groupby(grouper(ddf))), func(pdf.groupby(grouper(pdf))))

        # SeriesGroupBy
        assert_eq(
            func(ddf.groupby(grouper(ddf))["B"]), func(pdf.groupby(grouper(pdf))["B"])
        )

        # DataFrameGroupBy with column slice
        assert_eq(
            func(ddf.groupby(grouper(ddf))[["B", "C"]]),
            func(pdf.groupby(grouper(pdf))[["B", "C"]]),
        )


def test_numeric_column_names():
    # df.groupby(0)[df.columns] fails if all columns are numbers (pandas bug)
    # This ensures that we cast all column iterables to list beforehand.
    df = pd.DataFrame({0: [0, 1, 0, 1], 1: [1, 2, 3, 4], 2: [0, 1, 0, 1]})
    ddf = dd.from_pandas(df, npartitions=2)
    assert_eq(ddf.groupby(0).sum(), df.groupby(0).sum())
    assert_eq(ddf.groupby([0, 2]).sum(), df.groupby([0, 2]).sum())
    expected = df.groupby(0).apply(lambda x: x, **INCLUDE_GROUPS)
    assert_eq(
        ddf.groupby(0).apply(lambda x: x, meta=expected, **INCLUDE_GROUPS),
        expected,
    )


def test_groupby_apply_tasks(shuffle_method):
    if shuffle_method == "disk":
        pytest.skip("Tasks-only shuffle test")

    df = _compat.makeTimeDataFrame()
    df["A"] = df.A // 0.1
    df["B"] = df.B // 0.1
    ddf = dd.from_pandas(df, npartitions=10)

    for ind in [lambda x: "A", lambda x: x.A]:
        a = df.groupby(ind(df)).apply(len, **INCLUDE_GROUPS)
        with pytest.warns(UserWarning):
            b = ddf.groupby(ind(ddf)).apply(len, **INCLUDE_GROUPS)
        assert_eq(a, b.compute())
        assert not any("partd" in k[0] for k in b.dask)

        a = df.groupby(ind(df)).B.apply(len, **INCLUDE_GROUPS)
        with pytest.warns(UserWarning):
            b = ddf.groupby(ind(ddf)).B.apply(len, **INCLUDE_GROUPS)
        assert_eq(a, b.compute())
        assert not any("partd" in k[0] for k in b.dask)


def test_groupby_multiprocessing():
    df = pd.DataFrame({"A": [1, 2, 3, 4, 5], "B": ["1", "1", "a", "a", "a"]})

    ddf = dd.from_pandas(df, npartitions=3)
    expected = df.groupby("B").apply(lambda x: x, **INCLUDE_GROUPS)
    # since we explicitly provide meta, we have to convert it to pyarrow strings
    meta = to_pyarrow_string(expected) if pyarrow_strings_enabled() else expected
    with dask.config.set(scheduler="processes"):
        assert_eq(
            ddf.groupby("B").apply(lambda x: x, meta=meta, **INCLUDE_GROUPS),
            expected,
        )


def test_groupby_normalize_by():
    full = pd.DataFrame(
        {"a": [1, 2, 3, 4, 5, 6, 7, 8, 9], "b": [4, 5, 6, 3, 2, 1, 0, 0, 0]},
        index=[0, 1, 3, 5, 6, 8, 9, 9, 9],
    )
    d = dd.from_pandas(full, npartitions=3)

    assert d.groupby("a").by == ["a"]
    assert d.groupby(d["a"]).by == ["a"]
    assert d.groupby(["a", "b"]).by == ["a", "b"]

    assert d.groupby([d["a"], d["b"]]).by == ["a", "b"]
    assert d.groupby([d["a"], "b"]).by == ["a", "b"]


def test_aggregate_single_element_groups(agg_func):
    spec = agg_func

    # nunique/cov is not supported in specs
    if spec in ("nunique", "cov", "corr"):
        return

    pdf = pd.DataFrame(
        {"a": [1, 1, 3, 3], "b": [4, 4, 16, 16], "c": [1, 1, 4, 4], "d": [1, 1, 3, 3]},
        columns=["c", "b", "a", "d"],
    )
    ddf = dd.from_pandas(pdf, npartitions=3)

    expected = pdf.groupby(["a", "d"]).agg(spec)

    # NOTE: for std the result is not recast to the original dtype
    if spec in {"mean", "var"}:
        expected = expected.astype(float)

    shuffle_method = (
        {"shuffle_method": "tasks", "split_out": 2} if agg_func == "median" else {}
    )
    assert_eq(expected, ddf.groupby(["a", "d"]).agg(spec, **shuffle_method))


def test_aggregate_build_agg_args__reuse_of_intermediates():
    """Aggregate reuses intermediates. For example, with sum, count, and mean
    the sums and counts are only calculated once across the graph and reused to
    compute the mean.
    """
    from dask.dataframe.groupby import _build_agg_args

    no_mean_spec = [("foo", "sum", "input"), ("bar", "count", "input")]

    with_mean_spec = [
        ("foo", "sum", "input"),
        ("bar", "count", "input"),
        ("baz", "mean", "input"),
    ]

    no_mean_chunks, no_mean_aggs, no_mean_finalizers = _build_agg_args(no_mean_spec)
    with_mean_chunks, with_mean_aggs, with_mean_finalizers = _build_agg_args(
        with_mean_spec
    )

    assert len(no_mean_chunks) == len(with_mean_chunks)
    assert len(no_mean_aggs) == len(with_mean_aggs)

    assert len(no_mean_finalizers) == len(no_mean_spec)
    assert len(with_mean_finalizers) == len(with_mean_spec)


@pytest.mark.parametrize("split_every", [1, 8])
@pytest.mark.parametrize("split_out", [2, 32])
def test_shuffle_aggregate(shuffle_method, split_out, split_every):
    pdf = pd.DataFrame(
        {
            "a": [1, 2, 3, 1, 1, 2, 4, 3, 7] * 100,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 100,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 100,
            "d": [3, 2, 1, 3, 2, 1, 2, 6, 4] * 100,
        },
        columns=["c", "b", "a", "d"],
    )
    ddf = dd.from_pandas(pdf, npartitions=100)

    spec = {"b": "mean", "c": ["min", "max"]}
    result = ddf.groupby(["a", "b"], sort=False).agg(
        spec,
        split_out=split_out,
        split_every=split_every,
        shuffle_method=shuffle_method,
    )
    expect = pdf.groupby(["a", "b"]).agg(spec)

    # Make sure "mean" dtype is consistent.
    # Pandas<1.3 will return int instead of float
    expect[("b", "mean")] = expect[("b", "mean")].astype(result[("b", "mean")].dtype)
    assert_eq(expect, result)


@pytest.mark.parametrize("sort", [True, False])
def test_shuffle_aggregate_sort(shuffle_method, sort):
    pdf = pd.DataFrame(
        {
            "a": [1, 2, 3, 1, 1, 2, 4, 3, 7] * 100,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 100,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 100,
            "d": [3, 2, 1, 3, 2, 1, 2, 6, 4] * 100,
        },
        columns=["c", "b", "a", "d"],
    )
    ddf = dd.from_pandas(pdf, npartitions=100)

    # Check single-column groupby
    spec = {"b": "mean", "c": ["min", "max"]}
    result = ddf.groupby("a", sort=sort).agg(
        spec, split_out=2, shuffle_backend=shuffle_method
    )
    expect = pdf.groupby("a", sort=sort).agg(spec)
    assert_eq(expect, result)

    # Check multi-column groupby
    result = ddf.groupby(["a", "b"], sort=sort).agg(
        spec, split_out=2, shuffle_backend=shuffle_method
    )
    expect = pdf.groupby(["a", "b"], sort=sort).agg(spec)
    assert_eq(expect, result, sort_results=not sort)


def test_shuffle_aggregate_defaults(shuffle_method):
    pdf = pd.DataFrame(
        {
            "a": [1, 2, 3, 1, 1, 2, 4, 3, 7] * 100,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 100,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 100,
            "d": [3, 2, 1, 3, 2, 1, 2, 6, 4] * 100,
        },
        columns=["c", "b", "a", "d"],
    )
    ddf = dd.from_pandas(pdf, npartitions=100)

    spec = {"b": "mean", "c": ["min", "max"]}

    # split_every=1 is invalid for tree reduction
    with pytest.raises(ValueError):
        ddf.groupby("a").agg(spec, split_out=1, split_every=1).compute()


@pytest.mark.parametrize("spec", [{"c": "median"}, {"b": "median", "c": "max"}])
@pytest.mark.parametrize("keys", ["a", ["a", "d"]])
def test_aggregate_median(spec, keys, shuffle_method):
    pdf = pd.DataFrame(
        {
            "a": [1, 2, 3, 1, 1, 2, 4, 3, 7] * 10,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 10,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 10,
            "d": [3, 2, 1, 3, 2, 1, 2, 6, 4] * 10,
        },
        columns=["c", "b", "a", "d"],
    )
    ddf = dd.from_pandas(pdf, npartitions=10)
    actual = ddf.groupby(keys).aggregate(spec, shuffle_method=shuffle_method)
    expected = pdf.groupby(keys).aggregate(spec)
    assert_eq(actual, expected)


@pytest.mark.parametrize("group_keys", [True, False, None])
@pytest.mark.parametrize("limit", [None, 1, 4])
def test_ffill(group_keys, limit):
    df = pd.DataFrame(
        {
            "A": [1, 1, 2, 2],
            "B": [3, 4, 3, 4],
            "C": [np.nan, 3, np.nan, np.nan],
            "D": [4, np.nan, 5, np.nan],
            "E": [6, np.nan, 7, np.nan],
        }
    )
    ddf = dd.from_pandas(df, npartitions=2)
    assert_eq(
        df.groupby("A", group_keys=group_keys).ffill(limit=limit),
        ddf.groupby("A", group_keys=group_keys).ffill(limit=limit),
    )
    assert_eq(
        df.groupby("A", group_keys=group_keys).B.ffill(limit=limit),
        ddf.groupby("A", group_keys=group_keys).B.ffill(limit=limit),
    )
    assert_eq(
        df.groupby(["A", "B"], group_keys=group_keys).ffill(limit=limit),
        ddf.groupby(["A", "B"], group_keys=group_keys).ffill(limit=limit),
    )


@pytest.mark.parametrize("group_keys", [True, False, None])
@pytest.mark.parametrize("limit", [None, 1, 4])
def test_bfill(group_keys, limit):
    df = pd.DataFrame(
        {
            "A": [1, 1, 2, 2],
            "B": [3, 4, 3, 4],
            "C": [np.nan, 3, np.nan, np.nan],
            "D": [np.nan, 4, np.nan, 5],
            "E": [np.nan, 6, np.nan, 7],
        }
    )
    ddf = dd.from_pandas(df, npartitions=2)
    assert_eq(
        df.groupby("A", group_keys=group_keys).bfill(limit=limit),
        ddf.groupby("A", group_keys=group_keys).bfill(limit=limit),
    )
    assert_eq(
        df.groupby("A", group_keys=group_keys).B.bfill(limit=limit),
        ddf.groupby("A", group_keys=group_keys).B.bfill(limit=limit),
    )
    assert_eq(
        df.groupby(["A", "B"], group_keys=group_keys).bfill(limit=limit),
        ddf.groupby(["A", "B"], group_keys=group_keys).bfill(limit=limit),
    )


@pytest.mark.flaky(reruns=5)  # See https://github.com/dask/dask/issues/9793
@pytest.mark.parametrize(
    "grouper_id,grouper",
    [
        (0, lambda df: ["a"]),
        (1, lambda df: ["a", "b"]),
        (2, lambda df: df["a"]),
        (3, lambda df: [df["a"], df["b"]]),
        (4, lambda df: [df["a"] > 2, df["b"] > 1]),
    ],
)
@pytest.mark.parametrize("split_out", [1, 2])
def test_dataframe_aggregations_multilevel(
    xfail, grouper_id, grouper, agg_func, split_out
):
    if agg_func in ("cov", "corr") and split_out == 1 and grouper_id == 4:
        xfail("Unknown issue")
    elif agg_func in ("cov", "corr") and split_out > 1:
        xfail("https://github.com/dask/dask/issues/9509")

    sort = split_out == 1  # Don't sort for split_out > 1

    def call(g, m, **kwargs):
        return getattr(g, m)(**kwargs)

    pdf = pd.DataFrame(
        {
            "a": [1, 2, 6, 4, 4, 6, 4, 3, 7] * 10,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 10,
            "d": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 10,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 10,
        },
        columns=["c", "b", "a", "d"],
    )

    ddf = dd.from_pandas(pdf, npartitions=10)

    # covariance only works with N+1 columns
    if agg_func not in ("cov", "corr"):
        assert_eq(
            call(pdf.groupby(grouper(pdf), sort=sort)["c"], agg_func),
            call(
                ddf.groupby(grouper(ddf), sort=sort)["c"],
                agg_func,
                split_out=split_out,
                split_every=2,
            ),
        )

    # not supported by pandas
    if agg_func != "nunique":
        assert_eq(
            call(pdf.groupby(grouper(pdf), sort=sort)[["c", "d"]], agg_func),
            call(
                ddf.groupby(grouper(ddf), sort=sort)[["c", "d"]],
                agg_func,
                split_out=split_out,
                split_every=2,
            ),
        )

        if agg_func in ("cov", "corr"):
            # there are sorting issues between pandas and chunk cov w/dask
            df = call(pdf.groupby(grouper(pdf), sort=sort), agg_func).sort_index()
            cols = sorted(df.columns)
            df = df[cols]
            dddf = call(
                ddf.groupby(grouper(ddf), sort=sort),
                agg_func,
                split_out=split_out,
                split_every=2,
            ).compute()
            dddf = dddf.sort_index()
            cols = sorted(dddf.columns)
            dddf = dddf[cols]
            assert_eq(df, dddf)
        else:
            assert_eq(
                call(pdf.groupby(grouper(pdf), sort=sort), agg_func),
                call(
                    ddf.groupby(grouper(ddf), sort=sort),
                    agg_func,
                    split_out=split_out,
                    split_every=2,
                ),
            )


@pytest.mark.parametrize(
    "grouper",
    [
        lambda df: df["a"],
        lambda df: [df["a"], df["b"]],
        lambda df: [df["a"] > 2, df["b"] > 1],
    ],
)
@pytest.mark.parametrize("split_out", [1, 2])
def test_series_aggregations_multilevel(grouper, split_out, agg_func):
    """
    similar to ``test_dataframe_aggregations_multilevel``, but series do not
    support all groupby args.
    """
    sort = split_out == 1  # Don't sort for split_out > 1

    def call(g, m, **kwargs):
        return getattr(g, m)(**kwargs)

    # covariance/correlation is not a series aggregation
    if agg_func in ("cov", "corr"):
        return

    pdf = pd.DataFrame(
        {
            "a": [1, 2, 6, 4, 4, 6, 4, 3, 7] * 10,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 10,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 10,
        },
        columns=["c", "b", "a"],
    )

    ddf = dd.from_pandas(pdf, npartitions=10)

    assert_eq(
        call(pdf["c"].groupby(grouper(pdf), sort=sort), agg_func),
        call(
            ddf["c"].groupby(grouper(ddf), sort=sort),
            agg_func,
            split_out=split_out,
            split_every=2,
        ),
        # for pandas ~ 0.18, the name is not not properly propagated for
        # the mean aggregation
        check_names=(agg_func not in {"mean", "nunique"}),
    )


def test_groupy_non_aligned_index():
    pdf = pd.DataFrame(
        {
            "a": [1, 2, 6, 4, 4, 6, 4, 3, 7] * 10,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 10,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 10,
        },
        columns=["c", "b", "a"],
    )

    ddf3 = dd.from_pandas(pdf, npartitions=3)
    ddf7 = dd.from_pandas(pdf, npartitions=7)

    # working examples
    ddf3.groupby(["a", "b"])
    ddf3.groupby([ddf3["a"], ddf3["b"]])

    # misaligned divisions
    with pytest.raises(NotImplementedError):
        ddf3.groupby(ddf7["a"])

    with pytest.raises(NotImplementedError):
        ddf3.groupby([ddf7["a"], ddf7["b"]])

    with pytest.raises(NotImplementedError):
        ddf3.groupby([ddf7["a"], ddf3["b"]])

    with pytest.raises(NotImplementedError):
        ddf3.groupby([ddf3["a"], ddf7["b"]])

    with pytest.raises(NotImplementedError):
        ddf3.groupby([ddf7["a"], "b"])


def test_groupy_series_wrong_grouper():
    df = pd.DataFrame(
        {
            "a": [1, 2, 6, 4, 4, 6, 4, 3, 7] * 10,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 10,
            "c": [0, 1, 2, 3, 4, 5, 6, 7, 8] * 10,
        },
        columns=["c", "b", "a"],
    )

    df = dd.from_pandas(df, npartitions=3)
    s = df["a"]

    # working index values
    s.groupby(s)
    s.groupby([s, s])

    # non working index values
    with pytest.raises(KeyError):
        s.groupby("foo")

    with pytest.raises(KeyError):
        s.groupby([s, "foo"])

    with pytest.raises(ValueError):
        s.groupby(df)

    with pytest.raises(ValueError):
        s.groupby([s, df])


@pytest.mark.parametrize("npartitions", [1, 4, 20])
@pytest.mark.parametrize("split_every", [2, 5])
@pytest.mark.parametrize("split_out", [1, 5, 20])
def test_hash_groupby_aggregate(npartitions, split_every, split_out):
    df = pd.DataFrame({"x": np.arange(100) % 10, "y": np.ones(100)})
    ddf = dd.from_pandas(df, npartitions)

    result = ddf.groupby("x", sort=(split_out == 1)).y.var(
        split_every=split_every, split_out=split_out
    )

    assert result.npartitions == split_out

    assert_eq(result, df.groupby("x").y.var())


def test_split_out_multi_column_groupby():
    df = pd.DataFrame(
        {"x": np.arange(100) % 10, "y": np.ones(100), "z": [1, 2, 3, 4, 5] * 20}
    )

    ddf = dd.from_pandas(df, npartitions=10)

    result = ddf.groupby(["x", "y"], sort=False).z.mean(split_out=4)
    expected = df.groupby(["x", "y"]).z.mean()

    assert_eq(result, expected, check_dtype=False)


def test_groupby_split_out_num():
    # GH 1841
    ddf = dd.from_pandas(
        pd.DataFrame({"A": [1, 1, 2, 2], "B": [1, 2, 3, 4]}), npartitions=2
    )
    assert ddf.groupby("A").sum().npartitions == 1
    assert ddf.groupby("A", sort=False).sum(split_out=2).npartitions == 2
    assert ddf.groupby("A", sort=False).sum(split_out=3).npartitions == 3

    with pytest.raises(TypeError):
        # groupby doesn't accept split_out
        ddf.groupby("A", split_out=2)


def test_groupby_not_supported():
    ddf = dd.from_pandas(
        pd.DataFrame({"A": [1, 1, 2, 2], "B": [1, 2, 3, 4]}), npartitions=2
    )
    with pytest.raises(TypeError):
        ddf.groupby("A", axis=1)
    with pytest.raises(TypeError):
        ddf.groupby("A", level=1)
    with pytest.raises(TypeError):
        ddf.groupby("A", as_index=False)
    with pytest.raises(TypeError):
        ddf.groupby("A", squeeze=True)


def test_groupby_numeric_column():
    df = pd.DataFrame({"A": ["foo", "foo", "bar"], 0: [1, 2, 3]})
    ddf = dd.from_pandas(df, npartitions=3)

    assert_eq(ddf.groupby(ddf.A)[0].sum(), df.groupby(df.A)[0].sum())


@pytest.mark.skipif(
    WINDOWS and sys.version_info < (3, 11),
    reason="https://github.com/dask/dask/pull/11320#issuecomment-2293798597",
)
@pytest.mark.parametrize("sel", ["a", "c", "d", ["a", "b"], ["c", "d"]])
@pytest.mark.parametrize("key", ["a", ["a", "b"]])
@pytest.mark.parametrize("func", ["cumsum", "cumprod", "cumcount"])
def test_cumulative(func, key, sel):
    df = pd.DataFrame(
        {
            "a": [1, 2, 6, 4, 4, 6, 4, 3, 7] * 6,
            "b": [4, 2, 7, 3, 3, 1, 1, 1, 2] * 6,
            "c": np.random.randn(54),
            "d": np.random.randn(54),
        },
        columns=["a", "b", "c", "d"],
    )
    df.iloc[[-18, -12, -6], -1] = np.nan
    ddf = dd.from_pandas(df, npartitions=10)

    g, dg = (d.groupby(key)[sel] for d in (df, ddf))
    assert_eq(getattr(g, func)(), getattr(dg, func)())


def test_series_groupby_multi_character_column_name():
    df = pd.DataFrame({"aa": [1, 2, 1, 3, 4, 1, 2]})
    ddf = dd.from_pandas(df, npartitions=3)
    assert_eq(df.groupby("aa").aa.cumsum(), ddf.groupby("aa").aa.cumsum())


def test_groupby_unaligned_index():
    df = pd.DataFrame(
        {
            "a": np.random.randint(0, 10, 50),
            "b": np.random.randn(50),
            "c": np.random.randn(50),
        }
    )
    ddf = dd.from_pandas(df, npartitions=5)
    filtered = df[df.b < 0.5]
    dfiltered = ddf[ddf.b < 0.5]

    ddf_group = dfiltered.groupby(ddf.a)
    ds_group = dfiltered.b.groupby(ddf.a)

    bad = [
        ddf_group.mean(),
        ddf_group.var(),
        ddf_group.b.nunique(),
        ddf_group.get_group(0),
        ds_group.mean(),
        ds_group.var(),
        ds_group.nunique(),
        ds_group.get_group(0),
    ]

    for obj in bad:
        with pytest.raises(ValueError):
            obj.compute()

    def add1(x):
        return x + 1

    df_group = filtered.groupby(df.a)
    expected = df_group.apply(add1, **INCLUDE_GROUPS)
    assert_eq(ddf_group.apply(add1, meta=expected, **INCLUDE_GROUPS), expected)

    expected = df_group.b.apply(add1, **INCLUDE_GROUPS)
    assert_eq(ddf_group.b.apply(add1, meta=expected, **INCLUDE_GROUPS), expected)


def test_groupby_string_label():
    df = pd.DataFrame({"foo": [1, 1, 4], "B": [2, 3, 4], "C": [5, 6, 7]})
    ddf = dd.from_pandas(pd.DataFrame(df), npartitions=1)
    ddf_group = ddf.groupby("foo")
    result = ddf_group.get_group(1).compute()

    expected = pd.DataFrame(
        {"foo": [1, 1], "B": [2, 3], "C": [5, 6]}, index=pd.Index([0, 1])
    )

    tm.assert_frame_equal(result, expected)


@pytest.mark.skipif(
    WINDOWS and sys.version_info < (3, 11),
    reason="https://github.com/dask/dask/pull/11320#issuecomment-2293798597",
)
@pytest.mark.parametrize("op", ["cumsum", "cumprod"])
def test_groupby_dataframe_cum_caching(op):
    """Test caching behavior of cumulative operations on grouped dataframes.

    Relates to #3756.
    """
    df = pd.DataFrame(
        dict(a=list("aabbcc")), index=pd.date_range(start="20100101", periods=6)
    )
    df["ones"] = 1
    df["twos"] = 2

    ddf = dd.from_pandas(df, npartitions=3)

    ddf0 = getattr(ddf.groupby(["a"]), op)()
    ddf1 = ddf.rename(columns={"ones": "foo", "twos": "bar"})
    ddf1 = getattr(ddf1.groupby(["a"]), op)()

    # _a and _b dataframe should be equal
    res0_a, res1_a = dask.compute(ddf0, ddf1)
    res0_b, res1_b = ddf0.compute(), ddf1.compute()

    assert res0_a.equals(res0_b)
    assert res1_a.equals(res1_b)


def test_groupby_slice_agg_reduces():
    d = pd.DataFrame({"a": [1, 2, 3, 4], "b": [2, 3, 4, 5]})
    a = dd.from_pandas(d, npartitions=2)
    result = a.groupby("a")["b"].agg(["min", "max"])
    expected = d.groupby("a")["b"].agg(["min", "max"])
    assert_eq(result, expected)


def test_groupby_agg_grouper_single():
    # https://github.com/dask/dask/issues/2255
    d = pd.DataFrame({"a": [1, 2, 3, 4]})
    a = dd.from_pandas(d, npartitions=2)

    result = a.groupby("a")["a"].agg(["min", "max"])
    expected = d.groupby("a")["a"].agg(["min", "max"])
    assert_eq(result, expected)


@pytest.mark.parametrize("slice_", ["a", ["a"], ["a", "b"], ["b"]])
def test_groupby_agg_grouper_multiple(slice_):
    # https://github.com/dask/dask/issues/2255
    d = pd.DataFrame({"a": [1, 2, 3, 4], "b": [1, 2, 3, 4]})
    a = dd.from_pandas(d, npartitions=2)

    result = a.groupby("a")[slice_].agg(["min", "max"])
    expected = d.groupby("a")[slice_].agg(["min", "max"])
    assert_eq(result, expected)


@pytest.mark.skipif(
    WINDOWS and sys.version_info < (3, 11),
    reason="https://github.com/dask/dask/pull/11320#issuecomment-2293798597",
)
@pytest.mark.parametrize(
    "agg_func",
    [
        "cumprod",
        "cumcount",
        "cumsum",
        "var",
        "sum",
        "mean",
        "count",
        "size",
        "std",
        "min",
        "max",
        "first",
        "last",
        "prod",
    ],
)
def test_groupby_column_and_index_agg_funcs(agg_func):
    def call(g, m, **kwargs):
        return getattr(g, m)(**kwargs)

    df = pd.DataFrame(
        {
            "idx": [1, 1, 1, 2, 2, 2],
            "a": [1, 2, 1, 2, 1, 2],
            "b": np.arange(6),
            "c": [1, 1, 1, 2, 2, 2],
        }
    ).set_index("idx")

    ddf = dd.from_pandas(df, npartitions=df.index.nunique())
    ddf_no_divs = dd.from_pandas(df, npartitions=df.index.nunique(), sort=False)

    # Index and then column

    # Compute expected result
    expected = call(df.groupby(["idx", "a"]), agg_func)
    if agg_func in {"mean", "var"}:
        expected = expected.astype(float)

    result = call(ddf.groupby(["idx", "a"]), agg_func)
    assert_eq(expected, result)

    result = call(ddf_no_divs.groupby(["idx", "a"]), agg_func)
    assert_eq(expected, result)

    # apply-combine-apply aggregation functions
    aca_agg = {"sum", "mean", "var", "size", "std", "count", "first", "last", "prod"}

    # Test aggregate strings
    if agg_func in aca_agg:
        result = ddf_no_divs.groupby(["idx", "a"]).agg(agg_func)
        assert_eq(expected, result)

    # Column and then index

    # Compute expected result
    expected = call(df.groupby(["a", "idx"]), agg_func)
    if agg_func in {"mean", "var"}:
        expected = expected.astype(float)

    result = call(ddf.groupby(["a", "idx"]), agg_func)
    assert_eq(expected, result)

    result = call(ddf_no_divs.groupby(["a", "idx"]), agg_func)
    assert_eq(expected, result)

    # Test aggregate strings
    if agg_func in aca_agg:
        result = ddf_no_divs.groupby(["a", "idx"]).agg(agg_func)
        assert_eq(expected, result)

    # Index only

    # Compute expected result
    expected = call(df.groupby("idx"), agg_func)
    if agg_func in {"mean", "var"}:
        expected = expected.astype(float)

    result = call(ddf.groupby("idx"), agg_func)
    assert_eq(expected, result)

    result = call(ddf_no_divs.groupby("idx"), agg_func)
    assert_eq(expected, result)

    # Test aggregate strings
    if agg_func in aca_agg:
        result = ddf_no_divs.groupby("idx").agg(agg_func)
        assert_eq(expected, result)


@pytest.mark.parametrize("group_args", [["idx", "a"], ["a", "idx"], ["idx"], "idx"])
@pytest.mark.parametrize(
    "apply_func",
    [np.min, np.mean, lambda s, axis=None: np.max(s.values) - np.mean(s.values)],
)
def test_groupby_column_and_index_apply(group_args, apply_func):
    df = pd.DataFrame(
        {"idx": [1, 1, 1, 2, 2, 2], "a": [1, 2, 1, 2, 1, 2], "b": np.arange(6)}
    ).set_index("idx")

    ddf = dd.from_pandas(df, npartitions=df.index.nunique())
    ddf_no_divs = dd.from_pandas(
        df, npartitions=df.index.nunique(), sort=False
    ).clear_divisions()

    # Expected result
    expected = df.groupby(group_args).apply(apply_func, axis=0, **INCLUDE_GROUPS)

    # Compute on dask DataFrame with divisions (no shuffling)
    result = ddf.groupby(group_args).apply(
        apply_func, axis=0, meta=expected, **INCLUDE_GROUPS
    )
    assert_eq(expected, result, check_divisions=False)

    # Check that partitioning is preserved
    assert ddf.divisions == result.divisions

    # Check that no shuffling occurred.
    # The groupby operation should add only 1 task per partition
    assert len(result.dask) == (len(ddf.dask) + ddf.npartitions)

    expected = df.groupby(group_args).apply(apply_func, axis=0, **INCLUDE_GROUPS)

    # Compute on dask DataFrame without divisions (requires shuffling)
    result = ddf_no_divs.groupby(group_args).apply(
        apply_func, axis=0, meta=expected, **INCLUDE_GROUPS
    )

    assert_eq(expected, result, check_divisions=False)

    # Check that divisions were preserved (all None in this case)
    assert ddf_no_divs.divisions == result.divisions

    # Crude check to see if shuffling was performed.
    # The groupby operation should add only more than 1 task per partition
    assert len(result.dask) > (len(ddf_no_divs.dask) + ddf_no_divs.npartitions)


custom_mean = dd.Aggregation(
    "mean",
    lambda s: (s.count(), s.sum()),
    lambda s0, s1: (s0.sum(), s1.sum()),
    lambda s0, s1: s1 / s0,
)

custom_sum = dd.Aggregation("sum", lambda s: s.sum(), lambda s0: s0.sum())


@pytest.mark.parametrize(
    "pandas_spec, dask_spec, check_dtype",
    [
        ({"b": "mean"}, {"b": custom_mean}, False),
        ({"b": "sum"}, {"b": custom_sum}, True),
        (["mean", "sum"], [custom_mean, custom_sum], False),
        ({"b": ["mean", "sum"]}, {"b": [custom_mean, custom_sum]}, False),
    ],
)
def test_dataframe_groupby_agg_custom_sum(pandas_spec, dask_spec, check_dtype):
    df = pd.DataFrame({"g": [0, 0, 1] * 3, "b": [1, 2, 3] * 3})
    ddf = dd.from_pandas(df, npartitions=2)

    expected = df.groupby("g").aggregate(pandas_spec)
    result = ddf.groupby("g").aggregate(dask_spec)

    assert_eq(result, expected, check_dtype=check_dtype)


@pytest.mark.parametrize(
    "pandas_spec, dask_spec",
    [
        ("mean", custom_mean),
        (["mean"], [custom_mean]),
        (["mean", "sum"], [custom_mean, custom_sum]),
    ],
)
def test_series_groupby_agg_custom_mean(pandas_spec, dask_spec):
    d = pd.DataFrame({"g": [0, 0, 1] * 3, "b": [1, 2, 3] * 3})
    a = dd.from_pandas(d, npartitions=2)

    expected = d["b"].groupby(d["g"]).aggregate(pandas_spec)
    result = a["b"].groupby(a["g"]).aggregate(dask_spec)

    assert_eq(result, expected, check_dtype=False)


def test_groupby_agg_custom__name_clash_with_internal_same_column():
    """for a single input column only unique names are allowed"""
    d = pd.DataFrame({"g": [0, 0, 1] * 3, "b": [1, 2, 3] * 3})
    a = dd.from_pandas(d, npartitions=2)

    agg_func = dd.Aggregation("sum", lambda s: s.sum(), lambda s0: s0.sum())

    with pytest.raises(ValueError):
        a.groupby("g").aggregate({"b": [agg_func, "sum"]})


def test_groupby_agg_custom__name_clash_with_internal_different_column():
    """custom aggregation functions can share the name of a builtin function"""
    d = pd.DataFrame({"g": [0, 0, 1] * 3, "b": [1, 2, 3] * 3, "c": [4, 5, 6] * 3})
    a = dd.from_pandas(d, npartitions=2)

    # NOTE: this function is purposefully misnamed
    agg_func = dd.Aggregation(
        "sum",
        lambda s: (s.count(), s.sum()),
        lambda s0, s1: (s0.sum(), s1.sum()),
        lambda s0, s1: s1 / s0,
    )

    # NOTE: the name of agg-func is suppressed in the output,
    # since only a single agg func per column was specified
    result = a.groupby("g").aggregate({"b": agg_func, "c": "sum"})
    expected = d.groupby("g").aggregate({"b": "mean", "c": "sum"})

    assert_eq(result, expected, check_dtype=False)


def test_groupby_agg_custom__mode():
    # mode function passing intermediates as pure python objects around. to protect
    # results from pandas in apply use return results as single-item lists

    def agg_mode(s):
        def impl(s):
            (res,) = s.iloc[0]

            for (i,) in s.iloc[1:]:
                res = res.add(i, fill_value=0)

            return [res]

        return s.apply(impl, **INCLUDE_GROUPS)

    agg_func = dd.Aggregation(
        "custom_mode",
        lambda s: s.apply(lambda s: [s.value_counts()], **INCLUDE_GROUPS),
        agg_mode,
        lambda s: s.map(lambda i: i[0].idxmax()),
    )

    d = pd.DataFrame(
        {
            "g0": [0, 0, 0, 1, 1] * 3,
            "g1": [0, 0, 0, 1, 1] * 3,
            "cc": [4, 5, 4, 6, 6] * 3,
        }
    )
    a = dd.from_pandas(d, npartitions=5)

    actual = a["cc"].groupby([a["g0"], a["g1"]]).agg(agg_func)

    # cheat to get the correct index
    expected = pd.DataFrame({"g0": [0, 1], "g1": [0, 1], "cc": [4, 6]})
    expected = expected["cc"].groupby([expected["g0"], expected["g1"]]).agg("sum")

    assert_eq(actual, expected)


@pytest.mark.parametrize("func", ["var", list])
def test_groupby_select_column_agg(func):
    pdf = pd.DataFrame(
        {
            "A": [1, 2, 3, 1, 2, 3, 1, 2, 4],
            "B": [-0.776, -0.4, -0.873, 0.054, 1.419, -0.948, -0.967, -1.714, -0.666],
        }
    )
    ddf = dd.from_pandas(pdf, npartitions=4)
    actual = ddf.groupby("A")["B"].agg(func)
    expected = pdf.groupby("A")["B"].agg(func)
    assert_eq(actual, expected)


@contextlib.contextmanager
def record_numeric_only_warnings():
    with warnings.catch_warnings(record=True) as rec:
        warnings.filterwarnings(
            "always", "The default value of numeric_only", FutureWarning
        )
        yield rec


@pytest.mark.parametrize(
    "func",
    [
        pytest.param(
            "var",
            marks=pytest.mark.xfail(reason="numeric_only=False not implemented"),
        ),
        pytest.param(
            "std",
            marks=pytest.mark.xfail(reason="numeric_only=False not implemented"),
        ),
        pytest.param(
            "mean",
            marks=pytest.mark.xfail(reason="numeric_only=False not implemented"),
        ),
        pytest.param(
            "sum",
            marks=pytest.mark.xfail(
                pyarrow_strings_enabled() and not PANDAS_GE_230,
                reason="works in dask-expr",
            ),
        ),
    ],
)
def test_std_object_dtype(func):
    df = pd.DataFrame({"x": [1, 2, 1], "y": ["a", "b", "c"], "z": [11.0, 22.0, 33.0]})
    ddf = dd.from_pandas(df, npartitions=2)

    # DataFrame
    # TODO: add deprecation warnings to match pandas
    expected = getattr(df, func)()
    result = getattr(ddf, func)()
    assert_eq(expected, result)

    # DataFrameGroupBy
    with record_numeric_only_warnings() as rec_pd:
        expected = getattr(df.groupby("x"), func)()
    with record_numeric_only_warnings() as rec_dd:
        result = getattr(ddf.groupby("x"), func)()
    assert len(rec_pd) == len(rec_dd)
    assert_eq(expected, result)

    # SeriesGroupBy
    with record_numeric_only_warnings() as rec_pd:
        expected = getattr(df.groupby("x").z, func)()
    with record_numeric_only_warnings() as rec_dd:
        result = getattr(ddf.groupby("x").z, func)()
    assert len(rec_pd) == len(rec_dd)
    assert_eq(expected, result)


def test_std_columns_int():
    df = pd.DataFrame({0: [5], 1: [5]})
    ddf = dd.from_pandas(df, npartitions=2)
    assert_eq(ddf.groupby(ddf[0]).std(), df.groupby(df[0]).std())


def test_timeseries():
    df = dask.datasets.timeseries().partitions[:2]
    assert_eq(df.groupby("name").std(), df.groupby("name").std())


@pytest.mark.parametrize("min_count", [0, 1, 2, 3])
def test_with_min_count(min_count):
    dfs = [
        pd.DataFrame(
            {
                "group": ["A", "A", "B"],
                "val1": [np.nan, 2, 3],
                "val2": [np.nan, 5, 6],
                "val3": [5, 4, 9],
            }
        ),
        pd.DataFrame(
            {
                "group": ["A", "A", "B"],
                "val1": [2, np.nan, np.nan],
                "val2": [np.nan, 5, 6],
                "val3": [5, 4, 9],
            }
        ),
    ]
    ddfs = [dd.from_pandas(df, npartitions=4) for df in dfs]

    for df, ddf in zip(dfs, ddfs):
        assert_eq(
            df.groupby("group").sum(min_count=min_count),
            ddf.groupby("group").sum(min_count=min_count),
        )
        assert_eq(
            df.groupby("group").prod(min_count=min_count),
            ddf.groupby("group").prod(min_count=min_count),
        )


@pytest.mark.parametrize("group_keys", [True, False, None])
def test_groupby_group_keys(group_keys):
    df = pd.DataFrame({"a": [1, 2, 2, 3], "b": [2, 3, 4, 5]})
    ddf = dd.from_pandas(df, npartitions=2).set_index("a")
    pdf = df.set_index("a")

    func = lambda g: g.copy()
    expected = pdf.groupby("a").apply(func, **INCLUDE_GROUPS)
    assert_eq(expected, ddf.groupby("a").apply(func, meta=expected, **INCLUDE_GROUPS))

    expected = pdf.groupby("a", group_keys=group_keys).apply(func, **INCLUDE_GROUPS)
    assert_eq(
        expected,
        ddf.groupby("a", group_keys=group_keys).apply(
            func, meta=expected, **INCLUDE_GROUPS
        ),
    )


@pytest.mark.parametrize(
    "columns",
    [["a", "b", "c"], np.array([1.0, 2.0, 3.0]), ["1", "2", "3"], ["", "a", "b"]],
)
def test_groupby_cov(columns):
    rows = 20
    cols = 3
    data = np.random.randn(rows, cols)
    df = pd.DataFrame(data, columns=columns)
    df["key"] = [0] * 10 + [1] * 5 + [2] * 5
    ddf = dd.from_pandas(df, npartitions=3)

    expected = df.groupby("key").cov()
    result = ddf.groupby("key").cov()
    # when using numerical values for columns
    # the column mapping and stacking leads to a float typed
    # MultiIndex.  Pandas will normally create a object typed
    # MultiIndex
    if isinstance(columns, np.ndarray):
        result = result.compute()
        # don't bother checking index -- MultiIndex levels are in a frozenlist
        result.columns = result.columns.astype(np.dtype("O"))
        assert_eq(expected, result, check_index=False)
    else:
        assert_eq(expected, result)


def test_df_groupby_idxmin():
    pdf = pd.DataFrame(
        {"idx": list(range(4)), "group": [1, 1, 2, 2], "value": [10, 20, 20, 10]}
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=2)

    expected = pd.DataFrame({"group": [1, 2], "value": [0, 3]}).set_index("group")

    result_pd = pdf.groupby("group").idxmin()
    result_dd = ddf.groupby("group").idxmin()

    assert_eq(result_pd, result_dd)
    assert_eq(expected, result_dd)


@pytest.mark.parametrize("skipna", [True, False])
def test_df_groupby_idxmin_skipna(skipna):
    pdf = pd.DataFrame(
        {
            "idx": list(range(4)),
            "group": [1, 1, 2, 2],
            "value": [np.nan, 20.1, np.nan, 10.1],
        }
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=2)

    result_dd = ddf.groupby("group").idxmin(skipna=skipna)

    ctx = contextlib.nullcontext()
    if not skipna and PANDAS_GE_210 and not PANDAS_GE_300:
        ctx = pytest.warns(FutureWarning, match="all-NA values")
    elif not skipna and PANDAS_GE_300:
        ctx = pytest.raises(ValueError, match="encountered an NA")
    with ctx:
        result_pd = pdf.groupby("group").idxmin(skipna=skipna)
    if not skipna and PANDAS_GE_300:
        return
    with ctx:
        assert_eq(result_pd, result_dd)


def test_df_groupby_idxmax():
    pdf = pd.DataFrame(
        {"idx": list(range(4)), "group": [1, 1, 2, 2], "value": [10, 20, 20, 10]}
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=3)

    expected = pd.DataFrame({"group": [1, 2], "value": [1, 2]}).set_index("group")

    result_pd = pdf.groupby("group").idxmax()
    result_dd = ddf.groupby("group").idxmax()

    assert_eq(result_pd, result_dd)
    assert_eq(expected, result_dd)


@pytest.mark.parametrize("skipna", [True, False])
def test_df_groupby_idxmax_skipna(skipna):
    pdf = pd.DataFrame(
        {
            "idx": list(range(4)),
            "group": [1, 1, 2, 2],
            "value": [np.nan, 20.1, np.nan, 10.1],
        }
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=2)

    result_dd = ddf.groupby("group").idxmax(skipna=skipna)
    ctx = contextlib.nullcontext()
    if not skipna and PANDAS_GE_210 and not PANDAS_GE_300:
        ctx = pytest.warns(FutureWarning, match="all-NA values")
    elif not skipna and PANDAS_GE_300:
        ctx = pytest.raises(ValueError, match="encountered an NA")
    with ctx:
        result_pd = pdf.groupby("group").idxmax(skipna=skipna)
    if not skipna and PANDAS_GE_300:
        return
    with ctx:
        assert_eq(result_pd, result_dd)


def test_series_groupby_idxmin():
    pdf = pd.DataFrame(
        {"idx": list(range(4)), "group": [1, 1, 2, 2], "value": [10, 20, 20, 10]}
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=2)

    expected = (
        pd.DataFrame({"group": [1, 2], "value": [0, 3]}).set_index("group").squeeze()
    )

    result_pd = pdf.groupby("group")["value"].idxmin()
    result_dd = ddf.groupby("group")["value"].idxmin()

    assert_eq(result_pd, result_dd)
    assert_eq(expected, result_dd)


@pytest.mark.parametrize("skipna", [True, False])
def test_series_groupby_idxmin_skipna(skipna):
    pdf = pd.DataFrame(
        {
            "idx": list(range(4)),
            "group": [1, 1, 2, 2],
            "value": [np.nan, 20.1, np.nan, 10.1],
        }
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=2)

    result_dd = ddf.groupby("group")["value"].idxmin(skipna=skipna)
    ctx = contextlib.nullcontext()
    if not skipna and PANDAS_GE_210 and not PANDAS_GE_300:
        ctx = pytest.warns(FutureWarning, match="all-NA values")
    elif not skipna and PANDAS_GE_300:
        ctx = pytest.raises(ValueError, match="encountered an NA")
    with ctx:
        result_pd = pdf.groupby("group")["value"].idxmin(skipna=skipna)
    if not skipna and PANDAS_GE_300:
        return
    with ctx:
        assert_eq(result_pd, result_dd)


def test_series_groupby_idxmax():
    pdf = pd.DataFrame(
        {"idx": list(range(4)), "group": [1, 1, 2, 2], "value": [10, 20, 20, 10]}
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=3)

    expected = (
        pd.DataFrame({"group": [1, 2], "value": [1, 2]}).set_index("group").squeeze()
    )

    result_pd = pdf.groupby("group")["value"].idxmax()
    result_dd = ddf.groupby("group")["value"].idxmax()

    assert_eq(result_pd, result_dd)
    assert_eq(expected, result_dd)


@pytest.mark.parametrize("skipna", [True, False])
def test_series_groupby_idxmax_skipna(skipna):
    pdf = pd.DataFrame(
        {
            "idx": list(range(4)),
            "group": [1, 1, 2, 2],
            "value": [np.nan, 20.1, np.nan, 10.1],
        }
    ).set_index("idx")

    ddf = dd.from_pandas(pdf, npartitions=2)

    result_dd = ddf.groupby("group")["value"].idxmax(skipna=skipna)

    ctx = contextlib.nullcontext()
    if not skipna and PANDAS_GE_210 and not PANDAS_GE_300:
        ctx = pytest.warns(FutureWarning, match="all-NA values")
    elif not skipna and PANDAS_GE_300:
        ctx = pytest.raises(ValueError, match="encountered an NA")
    with ctx:
        result_pd = pdf.groupby("group")["value"].idxmax(skipna=skipna)
    if not skipna and PANDAS_GE_300:
        return
    with ctx:
        assert_eq(result_pd, result_dd)


@pytest.mark.skip_with_pyarrow_strings  # has to be array to explode
@pytest.mark.parametrize("int_dtype", ["uint8", "int32", "int64"])
def test_groupby_unique(int_dtype):
    rng = np.random.RandomState(42)
    df = pd.DataFrame(
        {"foo": rng.randint(3, size=100), "bar": rng.randint(10, size=100)},
        dtype=int_dtype,
    )

    ddf = dd.from_pandas(df, npartitions=10)

    pd_gb = df.groupby("foo")["bar"].unique()
    dd_gb = ddf.groupby("foo")["bar"].unique()

    # Use explode because each DataFrame row is a list; equality fails
    assert_eq(dd_gb.explode(), pd_gb.explode())


@pytest.mark.parametrize("by", ["foo", ["foo", "bar"]])
@pytest.mark.parametrize("int_dtype", ["uint8", "int32", "int64"])
def test_groupby_value_counts(by, int_dtype):
    rng = np.random.RandomState(42)
    df = pd.DataFrame(
        {
            "foo": rng.randint(3, size=100),
            "bar": rng.randint(4, size=100),
            "baz": rng.randint(5, size=100),
        },
        dtype=int_dtype,
    )
    ddf = dd.from_pandas(df, npartitions=2)

    pd_gb = df.groupby(by).baz.value_counts()
    dd_gb = ddf.groupby(by).baz.value_counts()
    assert_eq(dd_gb, pd_gb)


def test_groupby_value_counts_10322():
    """Repro case for https://github.com/dask/dask/issues/10322."""
    df = pd.DataFrame(
        {
            "x": [10] * 5 + [6] * 5 + [3] * 5,
            "y": [1] * 3 + [2] * 3 + [4] * 3 + [5] * 3 + [2] * 3,
        }
    )
    counts = df.groupby("x")["y"].value_counts()
    ddf = dd.from_pandas(df, npartitions=3)
    dcounts = ddf.groupby("x")["y"].value_counts()
    assert_eq(counts, dcounts)


@contextlib.contextmanager
def groupby_axis_and_meta(axis=0):
    # Because we're checking for multiple warnings, we need to record
    # all warnings and inspect them after the fact
    with pytest.warns() as record:
        yield
    expected_len = 1
    if axis == 1:
        expected_len += 1
    assert expected_len, [x.message for x in record.list]
    assert record[-1].category is UserWarning
    assert "`meta` is not specified" in str(record[-1].message)


def test_groupby_shift_series():
    pdf = pd.DataFrame(
        {
            "a": [0, 0, 1, 1, 2, 2, 3, 3, 3],
            "b": [4, 5, 6, 3, 2, 1, 0, 0, 0],
        },
    )
    ddf = dd.from_pandas(pdf, npartitions=3)
    with pytest.warns(UserWarning):
        assert_eq(
            pdf.groupby("a")["b"].shift(periods=2),
            ddf.groupby("a")["b"].shift(periods=2),
        )


@pytest.mark.xfail(reason="delayed not currently supported in here")
def test_groupby_shift_lazy_input():
    pdf = pd.DataFrame(
        {
            "a": [0, 0, 1, 1, 2, 2, 3, 3, 3],
            "b": [4, 5, 6, 3, 2, 1, 0, 0, 0],
            "c": [0, 0, 0, 0, 0, 1, 1, 1, 1],
        },
    )
    delayed_periods = dask.delayed(lambda: 1)()
    ddf = dd.from_pandas(pdf, npartitions=3)
    assert_eq(
        pdf.groupby(pdf.c).shift(periods=1),
        ddf.groupby(ddf.c).shift(periods=delayed_periods, meta={"a": int, "b": int}),
    )
    with pytest.warns(UserWarning):
        assert_eq(
            pdf.groupby(pdf.c).shift(periods=1, fill_value=pdf.b.max()),
            ddf.groupby(ddf.c).shift(periods=1, fill_value=ddf.b.max()),
        )


@pytest.mark.filterwarnings("ignore:`meta` is not specified")
def test_groupby_shift_within_partition_sorting():
    # Result is non-deterministic. We run the assertion a few times to keep
    # the probability of false pass low.
    for _ in range(10):
        df = pd.DataFrame(
            {
                "a": range(60),
                "b": [2, 4, 3, 1] * 15,
                "c": [None, 10, 20, None, 30, 40] * 10,
            }
        )
        df = df.set_index("a").sort_index()
        ddf = dd.from_pandas(df, npartitions=6)
        assert_eq(
            df.groupby("b")["c"].shift(1),
            ddf.groupby("b")["c"].shift(1),
            scheduler="threads",
        )


def test_groupby_shift_with_freq(shuffle_method):
    pdf = pd.DataFrame(
        dict(a=[1, 2, 3, 4, 5, 6], b=[0, 0, 0, 1, 1, 1]),
        index=pd.date_range(start="20100101", periods=6),
    )
    ddf = dd.from_pandas(pdf, npartitions=3)

    # just pass the pandas result as meta for convenience
    df_result = pdf.groupby(pdf.index).shift(periods=-2, freq="D")
    # Groupby/shift on the index should avoid shuffle and let the `freq` pass
    # unmodified, but that is currently broken: https://github.com/dask/dask/issues/8959
    # TODO: remove check_freq condition once fixed.
    assert_eq(
        df_result,
        ddf.groupby(ddf.index).shift(periods=-2, freq="D", meta=df_result),
        check_freq=False,
    )
    df_result = pdf.groupby("b").shift(periods=-2, freq="D")
    assert_eq(
        df_result,
        ddf.groupby("b").shift(periods=-2, freq="D", meta=df_result),
        # Somehow https://github.com/dask/dask/issues/10034 causes us to
        # drop the `freq`
        check_freq=shuffle_method != "disk",
    )


@pytest.mark.filterwarnings("ignore:`meta` is not specified")
# These warnings appear only on pandas >=2.1,<3.0
@pytest.mark.filterwarnings(r"ignore:.*(DataFrame|Series)GroupBy\.sum:FutureWarning")
@pytest.mark.filterwarnings(r"ignore:.*DataFrame\.sum with axis=None:FutureWarning")
@pytest.mark.parametrize(
    "transformation", [lambda x: x.sum(), np.sum, "sum", pd.Series.rank]
)
def test_groupby_transform_funcs(transformation):
    pdf = pd.DataFrame(
        {
            "A": [1, 2, 3, 4] * 5,
            "B": np.random.randn(20),
            "C": np.random.randn(20),
            "D": np.random.randn(20),
        }
    )
    ddf = dd.from_pandas(pdf, 3)

    # DataFrame
    assert_eq(
        pdf.groupby("A").transform(transformation),
        ddf.groupby("A").transform(transformation),
    )

    # Series
    assert_eq(
        pdf.groupby("A")["B"].transform(transformation),
        ddf.groupby("A")["B"].transform(transformation),
    )


@pytest.mark.parametrize("npartitions", list(range(1, 10)))
@pytest.mark.parametrize("indexed", [True, False], ids=["indexed", "not_indexed"])
def test_groupby_transform_ufunc_partitioning(npartitions, indexed):
    pdf = pd.DataFrame({"group": [1, 2, 3, 4, 5] * 20, "value": np.random.randn(100)})

    if indexed:
        pdf = pdf.set_index("group")

    ddf = dd.from_pandas(pdf, npartitions)

    with pytest.warns(UserWarning):
        # DataFrame
        assert_eq(
            pdf.groupby("group").transform(lambda series: series - series.mean()),
            ddf.groupby("group").transform(lambda series: series - series.mean()),
        )

        # Series
        assert_eq(
            pdf.groupby("group")["value"].transform(
                lambda series: series - series.mean()
            ),
            ddf.groupby("group")["value"].transform(
                lambda series: series - series.mean()
            ),
        )


@pytest.mark.parametrize(
    "grouping,agg",
    [
        (
            lambda df: df.drop(columns="category_2").groupby("category_1"),
            lambda grp: grp.mean(),
        ),
        (
            lambda df: df.drop(columns="category_2").groupby("category_1"),
            lambda grp: grp.agg("mean"),
        ),
        (
            lambda df: df.groupby(["category_1", "category_2"]),
            lambda grp: grp.mean(),
        ),
        (
            lambda df: df.groupby(["category_1", "category_2"]),
            lambda grp: grp.agg("mean"),
        ),
    ],
)
def test_groupby_aggregate_categoricals(grouping, agg):
    pdf = pd.DataFrame(
        {
            "category_1": pd.Categorical(list("AABBCC")),
            "category_2": pd.Categorical(list("ABCABC")),
            "value": np.random.uniform(size=6),
        }
    )
    ddf = dd.from_pandas(pdf, 2)

    # DataFrameGroupBy
    with check_observed_deprecation():
        expected = agg(grouping(pdf))

    observed_ctx = (
        pytest.warns(FutureWarning, match="observed")
        if PANDAS_GE_210 and not PANDAS_GE_300
        else contextlib.nullcontext()
    )
    with observed_ctx:
        result = agg(grouping(ddf))
        assert_eq(result, expected)

    # SeriesGroupBy
    with check_observed_deprecation():
        expected = agg(grouping(pdf)["value"])

    with observed_ctx:
        result = agg(grouping(ddf)["value"])
    assert_eq(result, expected)


@pytest.mark.parametrize(
    "agg",
    [
        lambda grp: grp.agg(partial(np.std, ddof=1)),
        lambda grp: grp.agg(partial(np.std, ddof=-2)),
        lambda grp: grp.agg(partial(np.var, ddof=1)),
        lambda grp: grp.agg(partial(np.var, ddof=-2)),
    ],
)
def test_groupby_aggregate_partial_function(agg):
    pdf = pd.DataFrame(
        {
            "a": [5, 4, 3, 5, 4, 2, 3, 2],
            "b": [1, 2, 5, 6, 9, 2, 6, 8],
        }
    )
    ddf = dd.from_pandas(pdf, npartitions=2)

    # DataFrameGroupBy
    assert_eq(agg(pdf.groupby("a")), agg(ddf.groupby("a")))

    # SeriesGroupBy
    assert_eq(agg(pdf.groupby("a")["b"]), agg(ddf.groupby("a")["b"]))


@pytest.mark.parametrize(
    "agg",
    [
        lambda grp: grp.agg(partial(np.std, unexpected_arg=1)),
        lambda grp: grp.agg(partial(np.var, unexpected_arg=1)),
    ],
)
def test_groupby_aggregate_partial_function_unexpected_kwargs(agg):
    pdf = pd.DataFrame(
        {
            "a": [5, 4, 3, 5, 4, 2, 3, 2],
            "b": [1, 2, 5, 6, 9, 2, 6, 8],
        }
    )
    ddf = dd.from_pandas(pdf, npartitions=2)

    with pytest.raises(
        TypeError,
        match=(
            "supports {'ddof'} keyword arguments, but got {'unexpected_arg'}|"
            "unexpected keyword argument 'unexpected_arg'"
        ),
    ):
        agg(ddf.groupby("a"))

    # SeriesGroupBy
    with pytest.raises(
        TypeError,
        match=(
            "supports {'ddof'} keyword arguments, but got {'unexpected_arg'}|"
            "unexpected keyword argument 'unexpected_arg'"
        ),
    ):
        agg(ddf.groupby("a")["b"])


@pytest.mark.parametrize(
    "agg",
    [
        lambda grp: grp.agg(partial(np.std, "positional_arg")),
        lambda grp: grp.agg(partial(np.var, "positional_arg")),
    ],
)
def test_groupby_aggregate_partial_function_unexpected_args(agg):
    pdf = pd.DataFrame(
        {
            "a": [5, 4, 3, 5, 4, 2, 3, 2],
            "b": [1, 2, 5, 6, 9, 2, 6, 8],
        }
    )
    ddf = dd.from_pandas(pdf, npartitions=2)

    with pytest.raises(
        TypeError,
        match=(
            "doesn't support positional arguments"
            "|'Series' object cannot be interpreted as an integer"
            "|cannot convert the series to <class 'int'>"
        ),
    ):
        agg(ddf.groupby("a"))

    # SeriesGroupBy
    with pytest.raises(
        TypeError,
        match=(
            "doesn't support positional arguments"
            "|'Series' object cannot be interpreted as an integer"
            "|cannot convert the series to <class 'int'>"
        ),
    ):
        agg(ddf.groupby("a")["b"])


@pytest.mark.parametrize("dropna", [False, True])
def test_groupby_dropna_pandas(dropna):
    df = pd.DataFrame(
        {"a": [1, 2, 3, 4, None, None, 7, 8], "e": [4, 5, 6, 3, 2, 1, 0, 0]}
    )
    ddf = dd.from_pandas(df, npartitions=3)

    dask_result = ddf.groupby("a", dropna=dropna).e.sum()
    pd_result = df.groupby("a", dropna=dropna).e.sum()
    assert_eq(dask_result, pd_result)


@pytest.mark.gpu
@pytest.mark.parametrize("dropna", [False, True, None])
@pytest.mark.parametrize("by", ["a", "c", "d", ["a", "b"], ["a", "c"], ["a", "d"]])
@pytest.mark.parametrize(
    "group_keys",
    [
        True,
        False,
        None,
    ],
)
def test_groupby_dropna_cudf(dropna, by, group_keys):
    # NOTE: This test requires cudf/dask_cudf, and will
    # be skipped by non-GPU CI

    cudf = pytest.importorskip("cudf")
    dask_cudf = pytest.importorskip("dask_cudf")

    df = cudf.DataFrame(
        {
            "a": [1, 2, 3, 4, None, None, 7, 8],
            "b": [1, 0] * 4,
            "c": ["a", "b", None, None, "e", "f", "g", "h"],
            "e": [4, 5, 6, 3, 2, 1, 0, 0],
        }
    )
    df["d"] = df["c"].astype("category")
    ddf = dask_cudf.from_cudf(df, npartitions=3)

    if dropna is None:
        dask_result = ddf.groupby(by, group_keys=group_keys).e.sum()
        cudf_result = df.groupby(by, group_keys=group_keys).e.sum()
    else:
        dask_result = ddf.groupby(by, dropna=dropna, group_keys=group_keys).e.sum()
        cudf_result = df.groupby(by, dropna=dropna, group_keys=group_keys).e.sum()
    if by in ["c", "d"]:
        # Lose string/category index name in cudf...
        dask_result = dask_result.compute()
        dask_result.index.name = cudf_result.index.name

    assert_eq(dask_result, cudf_result)


@pytest.mark.gpu
@pytest.mark.parametrize("key", ["a", "b"])
def test_groupby_grouper_dispatch(key):
    cudf = pytest.importorskip("cudf")

    # not directly used but must be imported
    pytest.importorskip("dask_cudf")

    pdf = pd.DataFrame(
        {
            "a": ["a", "b", "c", "d", "e", "f", "g", "h"],
            "b": [1, 2, 3, 4, 5, 6, 7, 8],
            "c": [1.0, 2.0, 3.5, 4.1, 5.5, 6.6, 7.9, 8.8],
        }
    )
    gdf = cudf.from_pandas(pdf)

    pd_grouper = grouper_dispatch(pdf)(key=key)
    gd_grouper = grouper_dispatch(gdf)(key=key)

    expect = pdf.groupby(pd_grouper).sum(numeric_only=True)
    got = gdf.groupby(gd_grouper).sum(numeric_only=True)

    assert_eq(expect, got)


@pytest.mark.gpu
@pytest.mark.parametrize(
    "group_keys",
    [
        True,
        False,
    ],
)
def test_groupby_apply_cudf(group_keys):
    # Check that groupby-apply is consistent between
    # 'pandas' and 'cudf' backends, and that the
    # implied shuffle works for the `cudf` backend

    # Make sure test is skipped without dask_cudf
    pytest.importorskip("dask_cudf")
    cudf = pytest.importorskip("cudf")

    df = pd.DataFrame({"a": [1, 2, 3, 1, 2, 3], "b": [4, 5, 6, 7, 8, 9]})
    ddf = dd.from_pandas(df, npartitions=2)
    dcdf = ddf.to_backend("cudf")

    func = lambda x: x
    res_pd = df.groupby("a", group_keys=group_keys).apply(func, **INCLUDE_GROUPS)
    res_dd = ddf.groupby("a", group_keys=group_keys).apply(
        func, meta=res_pd, **INCLUDE_GROUPS
    )
    res_dc = dcdf.groupby("a", group_keys=group_keys).apply(
        func, meta=cudf.from_pandas(res_pd), **INCLUDE_GROUPS
    )

    assert_eq(res_pd, res_dd)
    # Pandas and cudf return different `index.name`
    # for empty MultiIndex (use `check_names=False`)
    assert_eq(res_dd, res_dc, check_names=False)


@pytest.mark.parametrize("sort", [True, False])
def test_groupby_dropna_with_agg(sort):
    # https://github.com/dask/dask/issues/6986
    df = pd.DataFrame(
        {"id1": ["a", None, "b"], "id2": [1, 2, None], "v1": [4.5, 5.5, None]}
    )
    expected = df.groupby(["id1", "id2"], dropna=False, sort=sort).agg("sum")
    ddf = dd.from_pandas(df, 1)
    actual = ddf.groupby(["id1", "id2"], dropna=False, sort=sort).agg("sum")
    assert_eq(expected, actual)


def test_groupby_observed_with_agg():
    df = pd.DataFrame(
        {
            "cat_1": pd.Categorical(list("AB"), categories=list("ABCDE")),
            "cat_2": pd.Categorical([1, 2], categories=[1, 2, 3]),
            "value_1": np.random.uniform(size=2),
        }
    )
    expected = df.groupby(["cat_1", "cat_2"], observed=True).agg("sum")

    ddf = dd.from_pandas(df, 2)
    actual = ddf.groupby(["cat_1", "cat_2"], observed=True).agg("sum")
    assert_eq(expected, actual)


def test_rounding_negative_var():
    x = [-0.00179999999 for _ in range(10)]
    ids = [1 for _ in range(5)] + [2 for _ in range(5)]

    df = pd.DataFrame({"ids": ids, "x": x})

    ddf = dd.from_pandas(df, npartitions=2)
    assert_eq(ddf.groupby("ids").x.std(), df.groupby("ids").x.std())


@pytest.mark.parametrize("split_out", [2, 3])
@pytest.mark.parametrize("column", [["b", "c"], ["b", "d"], ["b", "e"]])
def test_groupby_split_out_multiindex(split_out, column):
    df = pd.DataFrame(
        {
            "a": np.arange(8),
            "b": [1, 0, 0, 2, 1, 1, 2, 0],
            "c": [0, 1] * 4,
            "d": ["dog", "cat", "cat", "dog", "dog", "dog", "cat", "bird"],
        }
    ).fillna(0)
    df["e"] = df["d"].astype("category")
    ddf = dd.from_pandas(df, npartitions=3)

    if column == ["b", "e"] and PANDAS_GE_210 and not PANDAS_GE_300:
        ctx = pytest.warns(FutureWarning, match="observed")
    else:
        ctx = contextlib.nullcontext()

    with ctx:
        result_so1 = (
            ddf.groupby(column, sort=False).a.mean(split_out=1).compute().dropna()
        )

        result = (
            ddf.groupby(column, sort=False)
            .a.mean(split_out=split_out)
            .compute()
            .dropna()
        )

    assert_eq(result, result_so1)


@pytest.mark.parametrize(
    "backend",
    [
        "pandas",
        pytest.param("cudf", marks=pytest.mark.gpu),
    ],
)
def test_groupby_large_ints_exception(backend):
    data_source = pytest.importorskip(backend)
    if backend == "cudf":
        dask_cudf = pytest.importorskip("dask_cudf")
        data_frame = dask_cudf.from_cudf
    else:
        data_frame = dd.from_pandas
    max = np.iinfo(np.uint64).max
    sqrt = max**0.5
    series = data_source.Series(
        np.concatenate([sqrt * np.arange(5), np.arange(35)])
    ).astype("int64")
    df = data_source.DataFrame({"x": series, "z": np.arange(40), "y": np.arange(40)})
    ddf = data_frame(df, npartitions=1)
    assert_eq(
        df.groupby("x").std(),
        ddf.groupby("x").std().compute(scheduler="single-threaded"),
    )


@pytest.mark.parametrize("by", ["a", "b", "c", ["a", "b"], ["a", "c"]])
@pytest.mark.parametrize(
    "agg",
    [
        "count",
        pytest.param(
            "mean", marks=pytest.mark.xfail(reason="numeric_only=False not implemented")
        ),
        pytest.param(
            "std", marks=pytest.mark.xfail(reason="numeric_only=False not implemented")
        ),
    ],
)
@pytest.mark.parametrize("sort", [True, False])
def test_groupby_sort_argument(by, agg, sort):
    df = pd.DataFrame(
        {
            "a": [1, 2, 3, 4, None, None, 7, 8],
            "b": [1, 0] * 4,
            "c": ["a", "b", None, None, "e", "f", "g", "h"],
            "e": [4, 5, 6, 3, 2, 1, 0, 0],
        }
    )
    ddf = dd.from_pandas(df, npartitions=3)

    gb = ddf.groupby(by, sort=sort)
    gb_pd = df.groupby(by, sort=sort)

    # Basic groupby aggregation
    result_1 = getattr(gb, agg)
    result_1_pd = getattr(gb_pd, agg)

    # Choose single column
    result_2 = getattr(gb.e, agg)
    result_2_pd = getattr(gb_pd.e, agg)

    # Use `agg()` api
    result_3 = gb.agg({"e": agg})
    result_3_pd = gb_pd.agg({"e": agg})

    if agg == "mean":
        with record_numeric_only_warnings() as rec_pd:
            expected = result_1_pd().astype("float")
        with record_numeric_only_warnings() as rec_dd:
            result = result_1()
        assert len(rec_pd) == len(rec_dd)
        assert_eq(result, expected)

        with record_numeric_only_warnings() as rec_pd:
            expected = result_2_pd().astype("float")
        with record_numeric_only_warnings() as rec_dd:
            result = result_2()
        assert len(rec_pd) == len(rec_dd)
        assert_eq(result, expected)

        with record_numeric_only_warnings() as rec_pd:
            expected = result_3_pd.astype("float")
        with record_numeric_only_warnings() as rec_dd:
            result = result_3
        assert len(rec_pd) == len(rec_dd)
        assert_eq(result, expected)
    else:
        with record_numeric_only_warnings() as rec_pd:
            expected = result_1_pd()
        with record_numeric_only_warnings() as rec_dd:
            result = result_1()
        assert len(rec_pd) == len(rec_dd)
        assert_eq(result, expected)

        with record_numeric_only_warnings() as rec_pd:
            expected = result_2_pd()
        with record_numeric_only_warnings() as rec_dd:
            result = result_2()
        assert len(rec_pd) == len(rec_dd)
        assert_eq(result, expected)

        with record_numeric_only_warnings() as rec_pd:
            expected = result_3_pd
        with record_numeric_only_warnings() as rec_dd:
            result = result_3
        assert len(rec_pd) == len(rec_dd)
        assert_eq(result, expected)


@pytest.mark.parametrize("agg", [M.sum, M.prod, M.max, M.min])
@pytest.mark.parametrize("sort", [True, False])
def test_groupby_sort_argument_agg(agg, sort):
    df = pd.DataFrame({"x": [4, 2, 1, 2, 3, 1], "y": [1, 2, 3, 4, 5, 6]})
    ddf = dd.from_pandas(df, npartitions=3)

    result = agg(ddf.groupby("x", sort=sort))
    result_pd = agg(df.groupby("x", sort=sort))

    assert_eq(result, result_pd)
    if sort:
        # Check order of index if sort==True
        # (no guarantee that order will match otherwise)
        assert_eq(result.index, result_pd.index)


def test_groupby_sort_true_split_out():
    df = pd.DataFrame({"x": [4, 2, 1, 2, 3, 1], "y": [1, 2, 3, 4, 5, 6]})
    ddf = dd.from_pandas(df, npartitions=3)

    # Works fine for split_out==1 or sort=False/None
    M.sum(ddf.groupby("x", sort=True), split_out=1)
    M.sum(ddf.groupby("x", sort=False), split_out=2)

    ddf.groupby("x").sum(split_out=2)
    ddf.groupby("x").agg("sum", split_out=2)

    # Can use sort=True with split_out>1 with agg() if shuffle=True
    ddf.groupby("x", sort=True).agg("sum", split_out=2, shuffle_method=True)


@pytest.mark.parametrize("known_cats", [True, False], ids=["known", "unknown"])
@pytest.mark.parametrize("ordered_cats", [True, False], ids=["ordered", "unordered"])
@pytest.mark.parametrize("groupby", ["cat_1", ["cat_1", "cat_2"]])
@pytest.mark.parametrize("observed", [True, False], ids=["observed", "unobserved"])
def test_groupby_aggregate_categorical_observed(
    xfail, agg_func, known_cats, ordered_cats, groupby, observed
):
    if agg_func in ("cov", "corr", "nunique"):
        xfail("Not implemented for DataFrameGroupBy yet.")
    elif (
        agg_func in ("mean", "median", "std", "sum", "var", "prod")
        and groupby == "cat_1"
    ):
        xfail("Can't calculate over categorical")
    elif agg_func == "median" and not observed:
        xfail("Unknown issue")
    elif agg_func == "prod" and not observed and not PANDAS_GE_300:
        xfail("Fixed in Pandas 3")

    pdf = pd.DataFrame(
        {
            "cat_1": pd.Categorical(
                list("AB"), categories=list("ABCDE"), ordered=ordered_cats
            ),
            "cat_2": pd.Categorical([1, 2], categories=[1, 2, 3], ordered=ordered_cats),
            "value_1": np.random.uniform(size=2),
        }
    )
    ddf = dd.from_pandas(pdf, 2)

    if not known_cats:
        ddf["cat_1"] = ddf["cat_1"].cat.as_unknown()
        ddf["cat_2"] = ddf["cat_2"].cat.as_unknown()

    def agg(grp, **kwargs):
        return getattr(grp, agg_func)(**kwargs)

    # only include numeric columns when passing to "min" or "max"
    # pandas default is numeric_only=False
    if ordered_cats is False and agg_func in ["min", "max"] and groupby == "cat_1":
        pdf = pdf[["cat_1", "value_1"]]
        ddf = ddf[["cat_1", "value_1"]]

    assert_eq(
        agg(pdf.groupby(groupby, observed=observed)),
        agg(ddf.groupby(groupby, observed=observed)),
    )


def test_groupby_cov_non_numeric_grouping_column():
    pdf = pd.DataFrame(
        {
            "a": 1,
            "b": [
                pd.Timestamp("2019-12-31"),
                pd.Timestamp("2019-12-31"),
                pd.Timestamp("2019-12-31"),
            ],
            "c": 2,
        }
    )

    ddf = dd.from_pandas(pdf, npartitions=2)
    assert_eq(ddf.groupby("b").cov(numeric_only=True), pdf.groupby("b").cov())


def test_groupby_numeric_only_None_column_name():
    df = pd.DataFrame({"a": [1, 2, 3], None: ["a", "b", "c"]})
    ddf = dd.from_pandas(df, npartitions=1)
    with pytest.raises(NotImplementedError):
        ddf.groupby(lambda x: x).mean(numeric_only=False)


@pytest.mark.parametrize("shuffle_method", [True, False])
def test_dataframe_named_agg(shuffle_method):
    df = pd.DataFrame(
        {
            "a": [1, 1, 2, 2],
            "b": [1, 2, 5, 6],
            "c": [6, 3, 6, 7],
        }
    )
    ddf = dd.from_pandas(df, npartitions=2)

    expected = df.groupby("a").agg(
        x=pd.NamedAgg("b", aggfunc="sum"),
        y=pd.NamedAgg("c", aggfunc=partial(np.std, ddof=1)),
    )
    actual = ddf.groupby("a").agg(
        shuffle_method=shuffle_method,
        x=pd.NamedAgg("b", aggfunc="sum"),
        y=pd.NamedAgg("c", aggfunc=partial(np.std, ddof=1)),
    )
    assert_eq(expected, actual)


@pytest.mark.parametrize("shuffle_method", [True, False])
@pytest.mark.parametrize("agg", ["count", "mean", partial(np.var, ddof=1)])
def test_series_named_agg(shuffle_method, agg):
    df = pd.DataFrame(
        {
            "a": [5, 4, 3, 5, 4, 2, 3, 2],
            "b": [1, 2, 5, 6, 9, 2, 6, 8],
        }
    )
    ddf = dd.from_pandas(df, npartitions=2)

    expected = df.groupby("a").b.agg(c=agg, d="sum")
    actual = ddf.groupby("a").b.agg(shuffle_method=shuffle_method, c=agg, d="sum")
    assert_eq(expected, actual)


@pytest.mark.parametrize("by", ["A", ["A", "B"]])
def test_empty_partitions_with_value_counts(by):
    # https://github.com/dask/dask/issues/7065
    df = pd.DataFrame(
        data=[
            ["a1", "b1", True],
            ["a1", None, False],
            ["a1", "b1", True],
            [None, None, None],
            [None, None, None],
            [None, None, None],
            ["a3", "b3", True],
            ["a3", "b3", False],
            ["a5", "b5", True],
        ],
        columns=["A", "B", "C"],
    )
    if pyarrow_strings_enabled():
        df = df.convert_dtypes()
    expected = df.groupby(by).C.value_counts()
    ddf = dd.from_pandas(df, npartitions=3)
    actual = ddf.groupby(by).C.value_counts()
    assert_eq(expected, actual)


def test_groupby_with_pd_grouper():
    ddf = dd.from_pandas(
        pd.DataFrame(
            {"key1": ["a", "b", "a"], "key2": ["c", "c", "c"], "value": [1, 2, 3]}
        ),
        npartitions=3,
    )
    with pytest.raises(NotImplementedError):
        ddf.groupby(pd.Grouper(key="key1"))
    with pytest.raises(NotImplementedError):
        ddf.groupby(["key1", pd.Grouper(key="key2")])


# TODO: Remove filter once https://github.com/pandas-dev/pandas/issues/46814 is resolved
@pytest.mark.filterwarnings("ignore:Invalid value encountered:RuntimeWarning")
@pytest.mark.parametrize("operation", ["head", "tail"])
def test_groupby_empty_partitions_with_rows_operation(operation):
    df = pd.DataFrame(
        data=[
            ["a1", "b1"],
            ["a1", None],
            ["a1", "b1"],
            [None, None],
            [None, None],
            [None, None],
            ["a3", "b3"],
            ["a3", "b3"],
            ["a5", "b5"],
        ],
        columns=["A", "B"],
    )

    caller = operator.methodcaller(operation, 1)
    expected = caller(df.groupby("A")["B"])
    ddf = dd.from_pandas(df, npartitions=3)
    actual = caller(ddf.groupby("A")["B"])
    assert_eq(expected, actual)


@pytest.mark.parametrize("operation", ["head", "tail"])
def test_groupby_with_row_operations(operation):
    df = pd.DataFrame(
        data=[
            ["a0", "b1"],
            ["a0", "b2"],
            ["a1", "b1"],
            ["a3", "b3"],
            ["a3", "b3"],
            ["a5", "b5"],
            ["a1", "b1"],
            ["a1", "b1"],
            ["a1", "b1"],
        ],
        columns=["A", "B"],
    )

    caller = operator.methodcaller(operation)
    expected = caller(df.groupby("A")["B"])
    ddf = dd.from_pandas(df, npartitions=3)
    actual = caller(ddf.groupby("A")["B"])
    assert_eq(expected, actual)


@pytest.mark.parametrize("operation", ["head", "tail"])
def test_groupby_multi_index_with_row_operations(operation):
    df = pd.DataFrame(
        data=[
            ["a0", "b1"],
            ["a0", "b2"],
            ["a1", "b1"],
            ["a3", "b3"],
            ["a3", "b3"],
            ["a5", "b5"],
            ["a1", "b1"],
            ["a1", "b1"],
            ["a1", "b1"],
        ],
        columns=["A", "B"],
    )

    caller = operator.methodcaller(operation)
    expected = caller(df.groupby(["A", df["A"].eq("a1")])["B"])
    ddf = dd.from_pandas(df, npartitions=3)
    actual = caller(ddf.groupby(["A", ddf["A"].eq("a1")])["B"])
    assert_eq(expected, actual)


def test_groupby_iter_fails():
    df = pd.DataFrame(
        data=[
            ["a0", "b1"],
            ["a1", "b1"],
            ["a3", "b3"],
            ["a5", "b5"],
        ],
        columns=["A", "B"],
    )
    ddf = dd.from_pandas(df, npartitions=1)
    with pytest.raises(KeyError, match="Column not"):
        list(ddf.groupby("A"))


@pytest.mark.parametrize("by", ["key1", ["key1", "key2"]])
@pytest.mark.parametrize(
    "slice_key",
    [
        3,
        "value",
        ["value"],
        ("value",),
        pd.Index(["value"]),
        pd.Series(["value"]),
    ],
)
def test_groupby_slice_getitem(by, slice_key):
    pdf = pd.DataFrame(
        {
            "key1": ["a", "b", "a"],
            "key2": ["c", "c", "c"],
            "value": [1, 2, 3],
            3: [1, 2, 3],
        }
    )

    ddf = dd.from_pandas(pdf, npartitions=3)
    expect = pdf.groupby(by)[slice_key].count()
    got = ddf.groupby(by)[slice_key].count()
    assert_eq(expect, got)


@pytest.mark.parametrize(
    "func",
    [
        "min",
        "max",
        "sum",
        "prod",
        "first",
        "last",
        "median",
        pytest.param(
            "idxmax",
            marks=pytest.mark.skip(reason="https://github.com/dask/dask/issues/9882"),
        ),
        pytest.param(
            "idxmin",
            marks=pytest.mark.skip(reason="https://github.com/dask/dask/issues/9882"),
        ),
    ],
)
@pytest.mark.parametrize(
    "numeric_only",
    [None, True, False],
)
def test_groupby_numeric_only_supported(func, numeric_only):
    pdf = pd.DataFrame(
        {
            "ints": [4, 4, 5, 5, 5],
            "ints2": [1, 2, 3, 4, 1],
            "dates": pd.date_range("2015-01-01", periods=5, freq="1min"),
            "strings": ["q", "c", "k", "a", "l"],
        }
    )
    ddf = dd.from_pandas(pdf, npartitions=3)

    kwargs = {} if numeric_only is None else {"numeric_only": numeric_only}

    ctx = contextlib.nullcontext()
    try:
        expected = getattr(pdf.groupby("ints"), func)(**kwargs)
        successful_compute = True
    except TypeError:
        # Make sure dask and pandas raise the same error message
        # We raise the error on _meta_nonempty, actual element may differ
        ctx = pytest.raises(
            TypeError,
            match="Cannot convert|could not convert|does not support|agg function failed",
        )
        successful_compute = False

    # Here's where we check that dask behaves the same as pandas
    with ctx:
        result = getattr(ddf.groupby("ints"), func)(**kwargs)
        if successful_compute:
            # expected is None if an error was raised
            assert_eq(expected, result)


@pytest.mark.parametrize("func", NUMERIC_ONLY_NOT_IMPLEMENTED)
@pytest.mark.parametrize("numeric_only", [False, None])
def test_groupby_numeric_only_not_implemented(func, numeric_only):
    """These should warn / error when numeric_only is set to its default / False"""
    df = pd.DataFrame({"A": [1, 1, 2], "B": [3, 4, 3], "C": ["a", "b", "c"]})
    ddf = dd.from_pandas(df, npartitions=3)

    ctx = pytest.raises(
        NotImplementedError, match="'numeric_only=False' is not implemented in Dask"
    )
    # Here `numeric_only=None` means "use default value for `numeric_only`"
    kwargs = {} if numeric_only is None else {"numeric_only": numeric_only}
    with ctx:
        getattr(ddf.groupby("A"), func)(**kwargs)


@pytest.mark.skipif(
    WINDOWS and sys.version_info < (3, 11),
    reason="https://github.com/dask/dask/pull/11320#issuecomment-2293798597",
)
@pytest.mark.parametrize(
    "func",
    [
        "min",
        "max",
        "sum",
        "prod",
        "first",
        "last",
        "corr",
        "cov",
        "cumprod",
        "cumsum",
        "mean",
        "median",
        "std",
        "var",
    ],
)
def test_groupby_numeric_only_true(func):
    df = pd.DataFrame({"A": [1, 1, 2, 2], "B": [3, 4, 3, 4], "C": ["a", "b", "c", "d"]})
    ddf = dd.from_pandas(df, npartitions=2)
    ddf_result = getattr(ddf.groupby("A"), func)(numeric_only=True)
    pdf_result = getattr(df.groupby("A"), func)(numeric_only=True)
    assert_eq(ddf_result, pdf_result)


@pytest.mark.parametrize("func", ["cov", "corr"])
def test_groupby_numeric_only_false_cov_corr(func):

    df = pd.DataFrame(
        {
            "float": [1.0, 2.0, 3.0, 4.0, 5, 6.0, 7.0, 8.0],
            "int": [1, 2, 3, 4, 5, 6, 7, 8],
            "A": 1,
        }
    )

    if not PANDAS_GE_300:
        # pandas 3.x doesn't support cov of datetime
        # https://github.com/pandas-dev/pandas/pull/60898
        df["timedelta"] = pd.to_timedelta([1, 2, 3, 4, 5, 6, 7, 8])

    ddf = dd.from_pandas(df, npartitions=2)
    dd_result = getattr(ddf.groupby("A"), func)(numeric_only=False)
    pd_result = getattr(df.groupby("A"), func)(numeric_only=False)
    assert_eq(dd_result, pd_result)

    dd_result = getattr(ddf.groupby("A"), func)(numeric_only=True)
    pd_result = getattr(df.groupby("A"), func)(numeric_only=True)
    assert_eq(dd_result, pd_result)


@pytest.mark.parametrize("func", ["cumsum", "cumprod"])
def test_groupby_numeric_only_false(func):
    df = pd.DataFrame(
        {
            "int": [1, 2, 3, 4, 5, 6, 7, 8],
            "float": [1.0, 2.0, 3.0, 4.0, np.nan, 6.0, 7.0, 8.0],
            "dt": [pd.NaT] + [datetime(2010, i, 1) for i in range(1, 8)],
            "A": 1,
        }
    )
    ddf = dd.from_pandas(df, npartitions=2)

    ctx = pytest.raises(TypeError, match="does not support")

    with ctx:
        getattr(ddf.groupby("A"), func)(numeric_only=False)
    with ctx:
        getattr(df.groupby("A"), func)(numeric_only=False)

    with ctx:
        getattr(ddf.groupby("A"), func)()
    with ctx:
        getattr(df.groupby("A"), func)()


@pytest.mark.parametrize("func", ["var", "std"])
@pytest.mark.parametrize("observed", [True, False])
@pytest.mark.parametrize("dropna", [True, False])
def test_groupby_var_dropna_observed(dropna, observed, func):
    df = pd.DataFrame(
        {
            "a": [11, 12, 31, 1, 2, 3, 4, 5, 6, 10],
            "b": pd.Categorical(values=[1] * 9 + [np.nan], categories=[1, 2]),
        }
    )
    ddf = dd.from_pandas(df, npartitions=3)
    dd_result = getattr(ddf.groupby("b", observed=observed, dropna=dropna), func)()
    pdf_result = getattr(df.groupby("b", observed=observed, dropna=dropna), func)()
    assert_eq(dd_result, pdf_result)


def test_groupby_value_counts_all_na_partitions():
    size = 100
    na_size = 90
    npartitions = 10

    df = pd.DataFrame(
        {
            "A": np.random.randint(0, 2, size=size, dtype=bool),
            "B": np.append(np.nan * np.zeros(na_size), np.random.randn(size - na_size)),
        }
    )
    ddf = dd.from_pandas(df, npartitions=npartitions)
    assert_eq(
        ddf.groupby("A")["B"].value_counts(),
        df.groupby("A")["B"].value_counts(),
    )


def test_agg_pyarrow_casts():
    pytest.importorskip("pyarrow")
    df = pd.DataFrame(
        {
            "x": range(15),
            "y": pd.Series([pd.NA] * 10 + [1.0] * 5, dtype="double[pyarrow]"),
            "group": ["a"] * 5 + ["b"] * 5 + ["c"] * 5,
        }
    )

    ddf = dd.from_pandas(df, npartitions=2)
    if PANDAS_GE_220:
        # np.sqrt doesn't work before 2.2
        additional_aggs = {"z": ("y", "std")}
    else:
        additional_aggs = {}

    result = ddf.groupby("group").agg(
        x=("y", "var"), y=("y", "mean"), **additional_aggs
    )
    expected = df.groupby("group").agg(
        x=("y", "var"), y=("y", "mean"), **additional_aggs
    )
    assert_eq(result, expected)
