import numpy as np
import pytest

import pandas.util._test_decorators as td

import pandas as pd
from pandas import DataFrame, Index, MultiIndex, Series
import pandas._testing as tm


class TestDataFrameSubclassing:
    def test_frame_subclassing_and_slicing(self):
        # Subclass frame and ensure it returns the right class on slicing it
        # In reference to PR 9632

        class CustomSeries(Series):
            @property
            def _constructor(self):
                return CustomSeries

            def custom_series_function(self):
                return "OK"

        class CustomDataFrame(DataFrame):
            """
            Subclasses pandas DF, fills DF with simulation results, adds some
            custom plotting functions.
            """

            def __init__(self, *args, **kw):
                super().__init__(*args, **kw)

            @property
            def _constructor(self):
                return CustomDataFrame

            _constructor_sliced = CustomSeries

            def custom_frame_function(self):
                return "OK"

        data = {"col1": range(10), "col2": range(10)}
        cdf = CustomDataFrame(data)

        # Did we get back our own DF class?
        assert isinstance(cdf, CustomDataFrame)

        # Do we get back our own Series class after selecting a column?
        cdf_series = cdf.col1
        assert isinstance(cdf_series, CustomSeries)
        assert cdf_series.custom_series_function() == "OK"

        # Do we get back our own DF class after slicing row-wise?
        cdf_rows = cdf[1:5]
        assert isinstance(cdf_rows, CustomDataFrame)
        assert cdf_rows.custom_frame_function() == "OK"

        # Make sure sliced part of multi-index frame is custom class
        mcol = pd.MultiIndex.from_tuples([("A", "A"), ("A", "B")])
        cdf_multi = CustomDataFrame([[0, 1], [2, 3]], columns=mcol)
        assert isinstance(cdf_multi["A"], CustomDataFrame)

        mcol = pd.MultiIndex.from_tuples([("A", ""), ("B", "")])
        cdf_multi2 = CustomDataFrame([[0, 1], [2, 3]], columns=mcol)
        assert isinstance(cdf_multi2["A"], CustomSeries)

    def test_dataframe_metadata(self):
        df = tm.SubclassedDataFrame(
            {"X": [1, 2, 3], "Y": [1, 2, 3]}, index=["a", "b", "c"]
        )
        df.testattr = "XXX"

        assert df.testattr == "XXX"
        assert df[["X"]].testattr == "XXX"
        assert df.loc[["a", "b"], :].testattr == "XXX"
        assert df.iloc[[0, 1], :].testattr == "XXX"

        # see gh-9776
        assert df.iloc[0:1, :].testattr == "XXX"

        # see gh-10553
        unpickled = tm.round_trip_pickle(df)
        tm.assert_frame_equal(df, unpickled)
        assert df._metadata == unpickled._metadata
        assert df.testattr == unpickled.testattr

    def test_indexing_sliced(self):
        # GH 11559
        df = tm.SubclassedDataFrame(
            {"X": [1, 2, 3], "Y": [4, 5, 6], "Z": [7, 8, 9]}, index=["a", "b", "c"]
        )
        res = df.loc[:, "X"]
        exp = tm.SubclassedSeries([1, 2, 3], index=list("abc"), name="X")
        tm.assert_series_equal(res, exp)
        assert isinstance(res, tm.SubclassedSeries)

        res = df.iloc[:, 1]
        exp = tm.SubclassedSeries([4, 5, 6], index=list("abc"), name="Y")
        tm.assert_series_equal(res, exp)
        assert isinstance(res, tm.SubclassedSeries)

        res = df.loc[:, "Z"]
        exp = tm.SubclassedSeries([7, 8, 9], index=list("abc"), name="Z")
        tm.assert_series_equal(res, exp)
        assert isinstance(res, tm.SubclassedSeries)

        res = df.loc["a", :]
        exp = tm.SubclassedSeries([1, 4, 7], index=list("XYZ"), name="a")
        tm.assert_series_equal(res, exp)
        assert isinstance(res, tm.SubclassedSeries)

        res = df.iloc[1, :]
        exp = tm.SubclassedSeries([2, 5, 8], index=list("XYZ"), name="b")
        tm.assert_series_equal(res, exp)
        assert isinstance(res, tm.SubclassedSeries)

        res = df.loc["c", :]
        exp = tm.SubclassedSeries([3, 6, 9], index=list("XYZ"), name="c")
        tm.assert_series_equal(res, exp)
        assert isinstance(res, tm.SubclassedSeries)

    def test_subclass_attr_err_propagation(self):
        # GH 11808
        class A(DataFrame):
            @property
            def bar(self):
                return self.i_dont_exist

        with pytest.raises(AttributeError, match=".*i_dont_exist.*"):
            A().bar

    def test_subclass_align(self):
        # GH 12983
        df1 = tm.SubclassedDataFrame(
            {"a": [1, 3, 5], "b": [1, 3, 5]}, index=list("ACE")
        )
        df2 = tm.SubclassedDataFrame(
            {"c": [1, 2, 4], "d": [1, 2, 4]}, index=list("ABD")
        )

        res1, res2 = df1.align(df2, axis=0)
        exp1 = tm.SubclassedDataFrame(
            {"a": [1, np.nan, 3, np.nan, 5], "b": [1, np.nan, 3, np.nan, 5]},
            index=list("ABCDE"),
        )
        exp2 = tm.SubclassedDataFrame(
            {"c": [1, 2, np.nan, 4, np.nan], "d": [1, 2, np.nan, 4, np.nan]},
            index=list("ABCDE"),
        )
        assert isinstance(res1, tm.SubclassedDataFrame)
        tm.assert_frame_equal(res1, exp1)
        assert isinstance(res2, tm.SubclassedDataFrame)
        tm.assert_frame_equal(res2, exp2)

        res1, res2 = df1.a.align(df2.c)
        assert isinstance(res1, tm.SubclassedSeries)
        tm.assert_series_equal(res1, exp1.a)
        assert isinstance(res2, tm.SubclassedSeries)
        tm.assert_series_equal(res2, exp2.c)

    def test_subclass_align_combinations(self):
        # GH 12983
        df = tm.SubclassedDataFrame({"a": [1, 3, 5], "b": [1, 3, 5]}, index=list("ACE"))
        s = tm.SubclassedSeries([1, 2, 4], index=list("ABD"), name="x")

        # frame + series
        res1, res2 = df.align(s, axis=0)
        exp1 = tm.SubclassedDataFrame(
            {"a": [1, np.nan, 3, np.nan, 5], "b": [1, np.nan, 3, np.nan, 5]},
            index=list("ABCDE"),
        )
        # name is lost when
        exp2 = tm.SubclassedSeries(
            [1, 2, np.nan, 4, np.nan], index=list("ABCDE"), name="x"
        )

        assert isinstance(res1, tm.SubclassedDataFrame)
        tm.assert_frame_equal(res1, exp1)
        assert isinstance(res2, tm.SubclassedSeries)
        tm.assert_series_equal(res2, exp2)

        # series + frame
        res1, res2 = s.align(df)
        assert isinstance(res1, tm.SubclassedSeries)
        tm.assert_series_equal(res1, exp2)
        assert isinstance(res2, tm.SubclassedDataFrame)
        tm.assert_frame_equal(res2, exp1)

    def test_subclass_iterrows(self):
        # GH 13977
        df = tm.SubclassedDataFrame({"a": [1]})
        for i, row in df.iterrows():
            assert isinstance(row, tm.SubclassedSeries)
            tm.assert_series_equal(row, df.loc[i])

    def test_subclass_stack(self):
        # GH 15564
        df = tm.SubclassedDataFrame(
            [[1, 2, 3], [4, 5, 6], [7, 8, 9]],
            index=["a", "b", "c"],
            columns=["X", "Y", "Z"],
        )

        res = df.stack()
        exp = tm.SubclassedSeries(
            [1, 2, 3, 4, 5, 6, 7, 8, 9], index=[list("aaabbbccc"), list("XYZXYZXYZ")]
        )

        tm.assert_series_equal(res, exp)

    def test_subclass_stack_multi(self):
        # GH 15564
        df = tm.SubclassedDataFrame(
            [[10, 11, 12, 13], [20, 21, 22, 23], [30, 31, 32, 33], [40, 41, 42, 43]],
            index=MultiIndex.from_tuples(
                list(zip(list("AABB"), list("cdcd"))), names=["aaa", "ccc"]
            ),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWXX"), list("yzyz"))), names=["www", "yyy"]
            ),
        )

        exp = tm.SubclassedDataFrame(
            [
                [10, 12],
                [11, 13],
                [20, 22],
                [21, 23],
                [30, 32],
                [31, 33],
                [40, 42],
                [41, 43],
            ],
            index=MultiIndex.from_tuples(
                list(zip(list("AAAABBBB"), list("ccddccdd"), list("yzyzyzyz"))),
                names=["aaa", "ccc", "yyy"],
            ),
            columns=Index(["W", "X"], name="www"),
        )

        res = df.stack()
        tm.assert_frame_equal(res, exp)

        res = df.stack("yyy")
        tm.assert_frame_equal(res, exp)

        exp = tm.SubclassedDataFrame(
            [
                [10, 11],
                [12, 13],
                [20, 21],
                [22, 23],
                [30, 31],
                [32, 33],
                [40, 41],
                [42, 43],
            ],
            index=MultiIndex.from_tuples(
                list(zip(list("AAAABBBB"), list("ccddccdd"), list("WXWXWXWX"))),
                names=["aaa", "ccc", "www"],
            ),
            columns=Index(["y", "z"], name="yyy"),
        )

        res = df.stack("www")
        tm.assert_frame_equal(res, exp)

    def test_subclass_stack_multi_mixed(self):
        # GH 15564
        df = tm.SubclassedDataFrame(
            [
                [10, 11, 12.0, 13.0],
                [20, 21, 22.0, 23.0],
                [30, 31, 32.0, 33.0],
                [40, 41, 42.0, 43.0],
            ],
            index=MultiIndex.from_tuples(
                list(zip(list("AABB"), list("cdcd"))), names=["aaa", "ccc"]
            ),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWXX"), list("yzyz"))), names=["www", "yyy"]
            ),
        )

        exp = tm.SubclassedDataFrame(
            [
                [10, 12.0],
                [11, 13.0],
                [20, 22.0],
                [21, 23.0],
                [30, 32.0],
                [31, 33.0],
                [40, 42.0],
                [41, 43.0],
            ],
            index=MultiIndex.from_tuples(
                list(zip(list("AAAABBBB"), list("ccddccdd"), list("yzyzyzyz"))),
                names=["aaa", "ccc", "yyy"],
            ),
            columns=Index(["W", "X"], name="www"),
        )

        res = df.stack()
        tm.assert_frame_equal(res, exp)

        res = df.stack("yyy")
        tm.assert_frame_equal(res, exp)

        exp = tm.SubclassedDataFrame(
            [
                [10.0, 11.0],
                [12.0, 13.0],
                [20.0, 21.0],
                [22.0, 23.0],
                [30.0, 31.0],
                [32.0, 33.0],
                [40.0, 41.0],
                [42.0, 43.0],
            ],
            index=MultiIndex.from_tuples(
                list(zip(list("AAAABBBB"), list("ccddccdd"), list("WXWXWXWX"))),
                names=["aaa", "ccc", "www"],
            ),
            columns=Index(["y", "z"], name="yyy"),
        )

        res = df.stack("www")
        tm.assert_frame_equal(res, exp)

    def test_subclass_unstack(self):
        # GH 15564
        df = tm.SubclassedDataFrame(
            [[1, 2, 3], [4, 5, 6], [7, 8, 9]],
            index=["a", "b", "c"],
            columns=["X", "Y", "Z"],
        )

        res = df.unstack()
        exp = tm.SubclassedSeries(
            [1, 4, 7, 2, 5, 8, 3, 6, 9], index=[list("XXXYYYZZZ"), list("abcabcabc")]
        )

        tm.assert_series_equal(res, exp)

    def test_subclass_unstack_multi(self):
        # GH 15564
        df = tm.SubclassedDataFrame(
            [[10, 11, 12, 13], [20, 21, 22, 23], [30, 31, 32, 33], [40, 41, 42, 43]],
            index=MultiIndex.from_tuples(
                list(zip(list("AABB"), list("cdcd"))), names=["aaa", "ccc"]
            ),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWXX"), list("yzyz"))), names=["www", "yyy"]
            ),
        )

        exp = tm.SubclassedDataFrame(
            [[10, 20, 11, 21, 12, 22, 13, 23], [30, 40, 31, 41, 32, 42, 33, 43]],
            index=Index(["A", "B"], name="aaa"),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWWWXXXX"), list("yyzzyyzz"), list("cdcdcdcd"))),
                names=["www", "yyy", "ccc"],
            ),
        )

        res = df.unstack()
        tm.assert_frame_equal(res, exp)

        res = df.unstack("ccc")
        tm.assert_frame_equal(res, exp)

        exp = tm.SubclassedDataFrame(
            [[10, 30, 11, 31, 12, 32, 13, 33], [20, 40, 21, 41, 22, 42, 23, 43]],
            index=Index(["c", "d"], name="ccc"),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWWWXXXX"), list("yyzzyyzz"), list("ABABABAB"))),
                names=["www", "yyy", "aaa"],
            ),
        )

        res = df.unstack("aaa")
        tm.assert_frame_equal(res, exp)

    def test_subclass_unstack_multi_mixed(self):
        # GH 15564
        df = tm.SubclassedDataFrame(
            [
                [10, 11, 12.0, 13.0],
                [20, 21, 22.0, 23.0],
                [30, 31, 32.0, 33.0],
                [40, 41, 42.0, 43.0],
            ],
            index=MultiIndex.from_tuples(
                list(zip(list("AABB"), list("cdcd"))), names=["aaa", "ccc"]
            ),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWXX"), list("yzyz"))), names=["www", "yyy"]
            ),
        )

        exp = tm.SubclassedDataFrame(
            [
                [10, 20, 11, 21, 12.0, 22.0, 13.0, 23.0],
                [30, 40, 31, 41, 32.0, 42.0, 33.0, 43.0],
            ],
            index=Index(["A", "B"], name="aaa"),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWWWXXXX"), list("yyzzyyzz"), list("cdcdcdcd"))),
                names=["www", "yyy", "ccc"],
            ),
        )

        res = df.unstack()
        tm.assert_frame_equal(res, exp)

        res = df.unstack("ccc")
        tm.assert_frame_equal(res, exp)

        exp = tm.SubclassedDataFrame(
            [
                [10, 30, 11, 31, 12.0, 32.0, 13.0, 33.0],
                [20, 40, 21, 41, 22.0, 42.0, 23.0, 43.0],
            ],
            index=Index(["c", "d"], name="ccc"),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWWWXXXX"), list("yyzzyyzz"), list("ABABABAB"))),
                names=["www", "yyy", "aaa"],
            ),
        )

        res = df.unstack("aaa")
        tm.assert_frame_equal(res, exp)

    def test_subclass_pivot(self):
        # GH 15564
        df = tm.SubclassedDataFrame(
            {
                "index": ["A", "B", "C", "C", "B", "A"],
                "columns": ["One", "One", "One", "Two", "Two", "Two"],
                "values": [1.0, 2.0, 3.0, 3.0, 2.0, 1.0],
            }
        )

        pivoted = df.pivot(index="index", columns="columns", values="values")

        expected = tm.SubclassedDataFrame(
            {
                "One": {"A": 1.0, "B": 2.0, "C": 3.0},
                "Two": {"A": 1.0, "B": 2.0, "C": 3.0},
            }
        )

        expected.index.name, expected.columns.name = "index", "columns"

        tm.assert_frame_equal(pivoted, expected)

    def test_subclassed_melt(self):
        # GH 15564
        cheese = tm.SubclassedDataFrame(
            {
                "first": ["John", "Mary"],
                "last": ["Doe", "Bo"],
                "height": [5.5, 6.0],
                "weight": [130, 150],
            }
        )

        melted = pd.melt(cheese, id_vars=["first", "last"])

        expected = tm.SubclassedDataFrame(
            [
                ["John", "Doe", "height", 5.5],
                ["Mary", "Bo", "height", 6.0],
                ["John", "Doe", "weight", 130],
                ["Mary", "Bo", "weight", 150],
            ],
            columns=["first", "last", "variable", "value"],
        )

        tm.assert_frame_equal(melted, expected)

    def test_subclassed_wide_to_long(self):
        # GH 9762

        np.random.seed(123)
        x = np.random.randn(3)
        df = tm.SubclassedDataFrame(
            {
                "A1970": {0: "a", 1: "b", 2: "c"},
                "A1980": {0: "d", 1: "e", 2: "f"},
                "B1970": {0: 2.5, 1: 1.2, 2: 0.7},
                "B1980": {0: 3.2, 1: 1.3, 2: 0.1},
                "X": dict(zip(range(3), x)),
            }
        )

        df["id"] = df.index
        exp_data = {
            "X": x.tolist() + x.tolist(),
            "A": ["a", "b", "c", "d", "e", "f"],
            "B": [2.5, 1.2, 0.7, 3.2, 1.3, 0.1],
            "year": [1970, 1970, 1970, 1980, 1980, 1980],
            "id": [0, 1, 2, 0, 1, 2],
        }
        expected = tm.SubclassedDataFrame(exp_data)
        expected = expected.set_index(["id", "year"])[["X", "A", "B"]]
        long_frame = pd.wide_to_long(df, ["A", "B"], i="id", j="year")

        tm.assert_frame_equal(long_frame, expected)

    def test_subclassed_apply(self):
        # GH 19822

        def check_row_subclass(row):
            assert isinstance(row, tm.SubclassedSeries)

        def strech(row):
            if row["variable"] == "height":
                row["value"] += 0.5
            return row

        df = tm.SubclassedDataFrame(
            [
                ["John", "Doe", "height", 5.5],
                ["Mary", "Bo", "height", 6.0],
                ["John", "Doe", "weight", 130],
                ["Mary", "Bo", "weight", 150],
            ],
            columns=["first", "last", "variable", "value"],
        )

        df.apply(lambda x: check_row_subclass(x))
        df.apply(lambda x: check_row_subclass(x), axis=1)

        expected = tm.SubclassedDataFrame(
            [
                ["John", "Doe", "height", 6.0],
                ["Mary", "Bo", "height", 6.5],
                ["John", "Doe", "weight", 130],
                ["Mary", "Bo", "weight", 150],
            ],
            columns=["first", "last", "variable", "value"],
        )

        result = df.apply(lambda x: strech(x), axis=1)
        assert isinstance(result, tm.SubclassedDataFrame)
        tm.assert_frame_equal(result, expected)

        expected = tm.SubclassedDataFrame([[1, 2, 3], [1, 2, 3], [1, 2, 3], [1, 2, 3]])

        result = df.apply(lambda x: tm.SubclassedSeries([1, 2, 3]), axis=1)
        assert isinstance(result, tm.SubclassedDataFrame)
        tm.assert_frame_equal(result, expected)

        result = df.apply(lambda x: [1, 2, 3], axis=1, result_type="expand")
        assert isinstance(result, tm.SubclassedDataFrame)
        tm.assert_frame_equal(result, expected)

        expected = tm.SubclassedSeries([[1, 2, 3], [1, 2, 3], [1, 2, 3], [1, 2, 3]])

        result = df.apply(lambda x: [1, 2, 3], axis=1)
        assert not isinstance(result, tm.SubclassedDataFrame)
        tm.assert_series_equal(result, expected)

    def test_subclassed_reductions(self, all_reductions):
        # GH 25596

        df = tm.SubclassedDataFrame({"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]})
        result = getattr(df, all_reductions)()
        assert isinstance(result, tm.SubclassedSeries)

    def test_subclassed_count(self):

        df = tm.SubclassedDataFrame(
            {
                "Person": ["John", "Myla", "Lewis", "John", "Myla"],
                "Age": [24.0, np.nan, 21.0, 33, 26],
                "Single": [False, True, True, True, False],
            }
        )
        result = df.count()
        assert isinstance(result, tm.SubclassedSeries)

        df = tm.SubclassedDataFrame({"A": [1, 0, 3], "B": [0, 5, 6], "C": [7, 8, 0]})
        result = df.count()
        assert isinstance(result, tm.SubclassedSeries)

        df = tm.SubclassedDataFrame(
            [[10, 11, 12, 13], [20, 21, 22, 23], [30, 31, 32, 33], [40, 41, 42, 43]],
            index=MultiIndex.from_tuples(
                list(zip(list("AABB"), list("cdcd"))), names=["aaa", "ccc"]
            ),
            columns=MultiIndex.from_tuples(
                list(zip(list("WWXX"), list("yzyz"))), names=["www", "yyy"]
            ),
        )
        result = df.count(level=1)
        assert isinstance(result, tm.SubclassedDataFrame)

        df = tm.SubclassedDataFrame()
        result = df.count()
        assert isinstance(result, tm.SubclassedSeries)

    def test_isin(self):

        df = tm.SubclassedDataFrame(
            {"num_legs": [2, 4], "num_wings": [2, 0]}, index=["falcon", "dog"]
        )
        result = df.isin([0, 2])
        assert isinstance(result, tm.SubclassedDataFrame)

    def test_duplicated(self):

        df = tm.SubclassedDataFrame({"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]})
        result = df.duplicated()
        assert isinstance(result, tm.SubclassedSeries)

        df = tm.SubclassedDataFrame()
        result = df.duplicated()
        assert isinstance(result, tm.SubclassedSeries)

    @pytest.mark.parametrize("idx_method", ["idxmax", "idxmin"])
    def test_idx(self, idx_method):

        df = tm.SubclassedDataFrame({"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]})
        result = getattr(df, idx_method)()
        assert isinstance(result, tm.SubclassedSeries)

    def test_dot(self):

        df = tm.SubclassedDataFrame([[0, 1, -2, -1], [1, 1, 1, 1]])
        s = tm.SubclassedSeries([1, 1, 2, 1])
        result = df.dot(s)
        assert isinstance(result, tm.SubclassedSeries)

        df = tm.SubclassedDataFrame([[0, 1, -2, -1], [1, 1, 1, 1]])
        s = tm.SubclassedDataFrame([1, 1, 2, 1])
        result = df.dot(s)
        assert isinstance(result, tm.SubclassedDataFrame)

    def test_memory_usage(self):

        df = tm.SubclassedDataFrame({"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]})
        result = df.memory_usage()
        assert isinstance(result, tm.SubclassedSeries)

        result = df.memory_usage(index=False)
        assert isinstance(result, tm.SubclassedSeries)

    @td.skip_if_no_scipy
    def test_corrwith(self):
        index = ["a", "b", "c", "d", "e"]
        columns = ["one", "two", "three", "four"]
        df1 = tm.SubclassedDataFrame(
            np.random.randn(5, 4), index=index, columns=columns
        )
        df2 = tm.SubclassedDataFrame(
            np.random.randn(4, 4), index=index[:4], columns=columns
        )
        correls = df1.corrwith(df2, axis=1, drop=True, method="kendall")

        assert isinstance(correls, (tm.SubclassedSeries))

    def test_asof(self):

        N = 3
        rng = pd.date_range("1/1/1990", periods=N, freq="53s")
        df = tm.SubclassedDataFrame(
            {
                "A": [np.nan, np.nan, np.nan],
                "B": [np.nan, np.nan, np.nan],
                "C": [np.nan, np.nan, np.nan],
            },
            index=rng,
        )

        result = df.asof(rng[-2:])
        assert isinstance(result, tm.SubclassedDataFrame)

        result = df.asof(rng[-2])
        assert isinstance(result, tm.SubclassedSeries)

        result = df.asof("1989-12-31")
        assert isinstance(result, tm.SubclassedSeries)

    def test_idxmin_preserves_subclass(self):
        # GH 28330

        df = tm.SubclassedDataFrame({"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]})
        result = df.idxmin()
        assert isinstance(result, tm.SubclassedSeries)

    def test_idxmax_preserves_subclass(self):
        # GH 28330

        df = tm.SubclassedDataFrame({"A": [1, 2, 3], "B": [4, 5, 6], "C": [7, 8, 9]})
        result = df.idxmax()
        assert isinstance(result, tm.SubclassedSeries)

    def test_equals_subclass(self):
        # https://github.com/pandas-dev/pandas/pull/34402
        # allow subclass in both directions
        df1 = pd.DataFrame({"a": [1, 2, 3]})
        df2 = tm.SubclassedDataFrame({"a": [1, 2, 3]})
        assert df1.equals(df2)
        assert df2.equals(df1)
