test_constructors.py

from datetime import datetime

import numpy as np
import pytest

from pandas.compat.numpy import _np_version_under1p16

from pandas.core.dtypes.common import is_float_dtype, is_integer_dtype
from pandas.core.dtypes.dtypes import CategoricalDtype

import pandas as pd
from pandas import (
    Categorical,
    CategoricalIndex,
    DatetimeIndex,
    Index,
    Interval,
    IntervalIndex,
    MultiIndex,
    NaT,
    Series,
    Timestamp,
    date_range,
    period_range,
    timedelta_range,
)
import pandas._testing as tm


class TestCategoricalConstructors:
    def test_validate_ordered(self):
        # see gh-14058
        exp_msg = "'ordered' must either be 'True' or 'False'"
        exp_err = TypeError

        # This should be a boolean.
        ordered = np.array([0, 1, 2])

        with pytest.raises(exp_err, match=exp_msg):
            Categorical([1, 2, 3], ordered=ordered)

        with pytest.raises(exp_err, match=exp_msg):
            Categorical.from_codes(
                [0, 0, 1], categories=["a", "b", "c"], ordered=ordered
            )

    def test_constructor_empty(self):
        # GH 17248
        c = Categorical([])
        expected = Index([])
        tm.assert_index_equal(c.categories, expected)

        c = Categorical([], categories=[1, 2, 3])
        expected = pd.Int64Index([1, 2, 3])
        tm.assert_index_equal(c.categories, expected)

    def test_constructor_empty_boolean(self):
        # see gh-22702
        cat = pd.Categorical([], categories=[True, False])
        categories = sorted(cat.categories.tolist())
        assert categories == [False, True]

    def test_constructor_tuples(self):
        values = np.array([(1,), (1, 2), (1,), (1, 2)], dtype=object)
        result = Categorical(values)
        expected = Index([(1,), (1, 2)], tupleize_cols=False)
        tm.assert_index_equal(result.categories, expected)
        assert result.ordered is False

    def test_constructor_tuples_datetimes(self):
        # numpy will auto reshape when all of the tuples are the
        # same len, so add an extra one with 2 items and slice it off
        values = np.array(
            [
                (Timestamp("2010-01-01"),),
                (Timestamp("2010-01-02"),),
                (Timestamp("2010-01-01"),),
                (Timestamp("2010-01-02"),),
                ("a", "b"),
            ],
            dtype=object,
        )[:-1]
        result = Categorical(values)
        expected = Index(
            [(Timestamp("2010-01-01"),), (Timestamp("2010-01-02"),)],
            tupleize_cols=False,
        )
        tm.assert_index_equal(result.categories, expected)

    def test_constructor_unsortable(self):

        # it works!
        arr = np.array([1, 2, 3, datetime.now()], dtype="O")
        factor = Categorical(arr, ordered=False)
        assert not factor.ordered

        # this however will raise as cannot be sorted
        msg = (
            "'values' is not ordered, please explicitly specify the "
            "categories order by passing in a categories argument."
        )
        with pytest.raises(TypeError, match=msg):
            Categorical(arr, ordered=True)

    def test_constructor_interval(self):
        result = Categorical(
            [Interval(1, 2), Interval(2, 3), Interval(3, 6)], ordered=True
        )
        ii = IntervalIndex([Interval(1, 2), Interval(2, 3), Interval(3, 6)])
        exp = Categorical(ii, ordered=True)
        tm.assert_categorical_equal(result, exp)
        tm.assert_index_equal(result.categories, ii)

    def test_constructor(self):

        exp_arr = np.array(["a", "b", "c", "a", "b", "c"], dtype=np.object_)
        c1 = Categorical(exp_arr)
        tm.assert_numpy_array_equal(c1.__array__(), exp_arr)
        c2 = Categorical(exp_arr, categories=["a", "b", "c"])
        tm.assert_numpy_array_equal(c2.__array__(), exp_arr)
        c2 = Categorical(exp_arr, categories=["c", "b", "a"])
        tm.assert_numpy_array_equal(c2.__array__(), exp_arr)

        # categories must be unique
        msg = "Categorical categories must be unique"
        with pytest.raises(ValueError, match=msg):
            Categorical([1, 2], [1, 2, 2])

        with pytest.raises(ValueError, match=msg):
            Categorical(["a", "b"], ["a", "b", "b"])

        # The default should be unordered
        c1 = Categorical(["a", "b", "c", "a"])
        assert not c1.ordered

        # Categorical as input
        c1 = Categorical(["a", "b", "c", "a"])
        c2 = Categorical(c1)
        tm.assert_categorical_equal(c1, c2)

        c1 = Categorical(["a", "b", "c", "a"], categories=["a", "b", "c", "d"])
        c2 = Categorical(c1)
        tm.assert_categorical_equal(c1, c2)

        c1 = Categorical(["a", "b", "c", "a"], categories=["a", "c", "b"])
        c2 = Categorical(c1)
        tm.assert_categorical_equal(c1, c2)

        c1 = Categorical(["a", "b", "c", "a"], categories=["a", "c", "b"])
        c2 = Categorical(c1, categories=["a", "b", "c"])
        tm.assert_numpy_array_equal(c1.__array__(), c2.__array__())
        tm.assert_index_equal(c2.categories, Index(["a", "b", "c"]))

        # Series of dtype category
        c1 = Categorical(["a", "b", "c", "a"], categories=["a", "b", "c", "d"])
        c2 = Categorical(Series(c1))
        tm.assert_categorical_equal(c1, c2)

        c1 = Categorical(["a", "b", "c", "a"], categories=["a", "c", "b"])
        c2 = Categorical(Series(c1))
        tm.assert_categorical_equal(c1, c2)

        # Series
        c1 = Categorical(["a", "b", "c", "a"])
        c2 = Categorical(Series(["a", "b", "c", "a"]))
        tm.assert_categorical_equal(c1, c2)

        c1 = Categorical(["a", "b", "c", "a"], categories=["a", "b", "c", "d"])
        c2 = Categorical(Series(["a", "b", "c", "a"]), categories=["a", "b", "c", "d"])
        tm.assert_categorical_equal(c1, c2)

        # This should result in integer categories, not float!
        cat = Categorical([1, 2, 3, np.nan], categories=[1, 2, 3])
        assert is_integer_dtype(cat.categories)

        # https://github.com/pandas-dev/pandas/issues/3678
        cat = Categorical([np.nan, 1, 2, 3])
        assert is_integer_dtype(cat.categories)

        # this should result in floats
        cat = Categorical([np.nan, 1, 2.0, 3])
        assert is_float_dtype(cat.categories)

        cat = Categorical([np.nan, 1.0, 2.0, 3.0])
        assert is_float_dtype(cat.categories)

        # This doesn't work -> this would probably need some kind of "remember
        # the original type" feature to try to cast the array interface result
        # to...

        # vals = np.asarray(cat[cat.notna()])
        # assert is_integer_dtype(vals)

        # corner cases
        cat = Categorical([1])
        assert len(cat.categories) == 1
        assert cat.categories[0] == 1
        assert len(cat.codes) == 1
        assert cat.codes[0] == 0

        cat = Categorical(["a"])
        assert len(cat.categories) == 1
        assert cat.categories[0] == "a"
        assert len(cat.codes) == 1
        assert cat.codes[0] == 0

        # Scalars should be converted to lists
        cat = Categorical(1)
        assert len(cat.categories) == 1
        assert cat.categories[0] == 1
        assert len(cat.codes) == 1
        assert cat.codes[0] == 0

        # two arrays
        #  - when the first is an integer dtype and the second is not
        #  - when the resulting codes are all -1/NaN
        with tm.assert_produces_warning(None):
            c_old = Categorical([0, 1, 2, 0, 1, 2], categories=["a", "b", "c"])  # noqa

        with tm.assert_produces_warning(None):
            c_old = Categorical([0, 1, 2, 0, 1, 2], categories=[3, 4, 5])  # noqa

        # the next one are from the old docs
        with tm.assert_produces_warning(None):
            c_old2 = Categorical([0, 1, 2, 0, 1, 2], [1, 2, 3])  # noqa
            cat = Categorical([1, 2], categories=[1, 2, 3])

        # this is a legitimate constructor
        with tm.assert_produces_warning(None):
            c = Categorical(  # noqa
                np.array([], dtype="int64"), categories=[3, 2, 1], ordered=True
            )

    def test_constructor_with_existing_categories(self):
        # GH25318: constructing with pd.Series used to bogusly skip recoding
        # categories
        c0 = Categorical(["a", "b", "c", "a"])
        c1 = Categorical(["a", "b", "c", "a"], categories=["b", "c"])

        c2 = Categorical(c0, categories=c1.categories)
        tm.assert_categorical_equal(c1, c2)

        c3 = Categorical(Series(c0), categories=c1.categories)
        tm.assert_categorical_equal(c1, c3)

    def test_constructor_not_sequence(self):
        # https://github.com/pandas-dev/pandas/issues/16022
        msg = r"^Parameter 'categories' must be list-like, was"
        with pytest.raises(TypeError, match=msg):
            Categorical(["a", "b"], categories="a")

    def test_constructor_with_null(self):

        # Cannot have NaN in categories
        msg = "Categorical categories cannot be null"
        with pytest.raises(ValueError, match=msg):
            Categorical([np.nan, "a", "b", "c"], categories=[np.nan, "a", "b", "c"])

        with pytest.raises(ValueError, match=msg):
            Categorical([None, "a", "b", "c"], categories=[None, "a", "b", "c"])

        with pytest.raises(ValueError, match=msg):
            Categorical(
                DatetimeIndex(["nat", "20160101"]),
                categories=[NaT, Timestamp("20160101")],
            )

    def test_constructor_with_index(self):
        ci = CategoricalIndex(list("aabbca"), categories=list("cab"))
        tm.assert_categorical_equal(ci.values, Categorical(ci))

        ci = CategoricalIndex(list("aabbca"), categories=list("cab"))
        tm.assert_categorical_equal(
            ci.values, Categorical(ci.astype(object), categories=ci.categories)
        )

    def test_constructor_with_generator(self):
        # This was raising an Error in isna(single_val).any() because isna
        # returned a scalar for a generator

        exp = Categorical([0, 1, 2])
        cat = Categorical((x for x in [0, 1, 2]))
        tm.assert_categorical_equal(cat, exp)
        cat = Categorical(range(3))
        tm.assert_categorical_equal(cat, exp)

        MultiIndex.from_product([range(5), ["a", "b", "c"]])

        # check that categories accept generators and sequences
        cat = Categorical([0, 1, 2], categories=(x for x in [0, 1, 2]))
        tm.assert_categorical_equal(cat, exp)
        cat = Categorical([0, 1, 2], categories=range(3))
        tm.assert_categorical_equal(cat, exp)

    @pytest.mark.parametrize(
        "dtl",
        [
            date_range("1995-01-01 00:00:00", periods=5, freq="s"),
            date_range("1995-01-01 00:00:00", periods=5, freq="s", tz="US/Eastern"),
            timedelta_range("1 day", periods=5, freq="s"),
        ],
    )
    def test_constructor_with_datetimelike(self, dtl):
        # see gh-12077
        # constructor with a datetimelike and NaT

        s = Series(dtl)
        c = Categorical(s)

        expected = type(dtl)(s)
        expected._data.freq = None

        tm.assert_index_equal(c.categories, expected)
        tm.assert_numpy_array_equal(c.codes, np.arange(5, dtype="int8"))

        # with NaT
        s2 = s.copy()
        s2.iloc[-1] = NaT
        c = Categorical(s2)

        expected = type(dtl)(s2.dropna())
        expected._data.freq = None

        tm.assert_index_equal(c.categories, expected)

        exp = np.array([0, 1, 2, 3, -1], dtype=np.int8)
        tm.assert_numpy_array_equal(c.codes, exp)

        result = repr(c)
        assert "NaT" in result

    def test_constructor_from_index_series_datetimetz(self):
        idx = date_range("2015-01-01 10:00", freq="D", periods=3, tz="US/Eastern")
        result = Categorical(idx)
        tm.assert_index_equal(result.categories, idx)

        result = Categorical(Series(idx))
        tm.assert_index_equal(result.categories, idx)

    def test_constructor_from_index_series_timedelta(self):
        idx = timedelta_range("1 days", freq="D", periods=3)
        result = Categorical(idx)
        tm.assert_index_equal(result.categories, idx)

        result = Categorical(Series(idx))
        tm.assert_index_equal(result.categories, idx)

    def test_constructor_from_index_series_period(self):
        idx = period_range("2015-01-01", freq="D", periods=3)
        result = Categorical(idx)
        tm.assert_index_equal(result.categories, idx)

        result = Categorical(Series(idx))
        tm.assert_index_equal(result.categories, idx)

    @pytest.mark.parametrize(
        "values",
        [
            np.array([1.0, 1.2, 1.8, np.nan]),
            np.array([1, 2, 3], dtype="int64"),
            ["a", "b", "c", np.nan],
            [pd.Period("2014-01"), pd.Period("2014-02"), NaT],
            [Timestamp("2014-01-01"), Timestamp("2014-01-02"), NaT],
            [
                Timestamp("2014-01-01", tz="US/Eastern"),
                Timestamp("2014-01-02", tz="US/Eastern"),
                NaT,
            ],
        ],
    )
    def test_constructor_invariant(self, values):
        # GH 14190
        c = Categorical(values)
        c2 = Categorical(c)
        tm.assert_categorical_equal(c, c2)

    @pytest.mark.parametrize("ordered", [True, False])
    def test_constructor_with_dtype(self, ordered):
        categories = ["b", "a", "c"]
        dtype = CategoricalDtype(categories, ordered=ordered)
        result = Categorical(["a", "b", "a", "c"], dtype=dtype)
        expected = Categorical(
            ["a", "b", "a", "c"], categories=categories, ordered=ordered
        )
        tm.assert_categorical_equal(result, expected)
        assert result.ordered is ordered

    def test_constructor_dtype_and_others_raises(self):
        dtype = CategoricalDtype(["a", "b"], ordered=True)
        msg = "Cannot specify `categories` or `ordered` together with `dtype`."
        with pytest.raises(ValueError, match=msg):
            Categorical(["a", "b"], categories=["a", "b"], dtype=dtype)

        with pytest.raises(ValueError, match=msg):
            Categorical(["a", "b"], ordered=True, dtype=dtype)

        with pytest.raises(ValueError, match=msg):
            Categorical(["a", "b"], ordered=False, dtype=dtype)

    @pytest.mark.parametrize("categories", [None, ["a", "b"], ["a", "c"]])
    @pytest.mark.parametrize("ordered", [True, False])
    def test_constructor_str_category(self, categories, ordered):
        result = Categorical(
            ["a", "b"], categories=categories, ordered=ordered, dtype="category"
        )
        expected = Categorical(["a", "b"], categories=categories, ordered=ordered)
        tm.assert_categorical_equal(result, expected)

    def test_constructor_str_unknown(self):
        with pytest.raises(ValueError, match="Unknown dtype"):
            Categorical([1, 2], dtype="foo")

    def test_constructor_np_strs(self):
        # GH#31499 Hastable.map_locations needs to work on np.str_ objects
        cat = pd.Categorical(["1", "0", "1"], [np.str_("0"), np.str_("1")])
        assert all(isinstance(x, np.str_) for x in cat.categories)

    def test_constructor_from_categorical_with_dtype(self):
        dtype = CategoricalDtype(["a", "b", "c"], ordered=True)
        values = Categorical(["a", "b", "d"])
        result = Categorical(values, dtype=dtype)
        # We use dtype.categories, not values.categories
        expected = Categorical(
            ["a", "b", "d"], categories=["a", "b", "c"], ordered=True
        )
        tm.assert_categorical_equal(result, expected)

    def test_constructor_from_categorical_with_unknown_dtype(self):
        dtype = CategoricalDtype(None, ordered=True)
        values = Categorical(["a", "b", "d"])
        result = Categorical(values, dtype=dtype)
        # We use values.categories, not dtype.categories
        expected = Categorical(
            ["a", "b", "d"], categories=["a", "b", "d"], ordered=True
        )
        tm.assert_categorical_equal(result, expected)

    def test_constructor_from_categorical_string(self):
        values = Categorical(["a", "b", "d"])
        # use categories, ordered
        result = Categorical(
            values, categories=["a", "b", "c"], ordered=True, dtype="category"
        )
        expected = Categorical(
            ["a", "b", "d"], categories=["a", "b", "c"], ordered=True
        )
        tm.assert_categorical_equal(result, expected)

        # No string
        result = Categorical(values, categories=["a", "b", "c"], ordered=True)
        tm.assert_categorical_equal(result, expected)

    def test_constructor_with_categorical_categories(self):
        # GH17884
        expected = Categorical(["a", "b"], categories=["a", "b", "c"])

        result = Categorical(["a", "b"], categories=Categorical(["a", "b", "c"]))
        tm.assert_categorical_equal(result, expected)

        result = Categorical(["a", "b"], categories=CategoricalIndex(["a", "b", "c"]))
        tm.assert_categorical_equal(result, expected)

    @pytest.mark.parametrize("klass", [lambda x: np.array(x, dtype=object), list])
    def test_construction_with_null(self, klass, nulls_fixture):
        # https://github.com/pandas-dev/pandas/issues/31927
        values = klass(["a", nulls_fixture, "b"])
        result = Categorical(values)

        dtype = CategoricalDtype(["a", "b"])
        codes = [0, -1, 1]
        expected = Categorical.from_codes(codes=codes, dtype=dtype)

        tm.assert_categorical_equal(result, expected)

    def test_from_codes_empty(self):
        cat = ["a", "b", "c"]
        result = Categorical.from_codes([], categories=cat)
        expected = Categorical([], categories=cat)

        tm.assert_categorical_equal(result, expected)

    def test_from_codes_too_few_categories(self):
        dtype = CategoricalDtype(categories=[1, 2])
        msg = "codes need to be between "
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes([1, 2], categories=dtype.categories)
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes([1, 2], dtype=dtype)

    def test_from_codes_non_int_codes(self):
        dtype = CategoricalDtype(categories=[1, 2])
        msg = "codes need to be array-like integers"
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes(["a"], categories=dtype.categories)
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes(["a"], dtype=dtype)

    def test_from_codes_non_unique_categories(self):
        with pytest.raises(ValueError, match="Categorical categories must be unique"):
            Categorical.from_codes([0, 1, 2], categories=["a", "a", "b"])

    def test_from_codes_nan_cat_included(self):
        with pytest.raises(ValueError, match="Categorical categories cannot be null"):
            Categorical.from_codes([0, 1, 2], categories=["a", "b", np.nan])

    def test_from_codes_too_negative(self):
        dtype = CategoricalDtype(categories=["a", "b", "c"])
        msg = r"codes need to be between -1 and len\(categories\)-1"
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes([-2, 1, 2], categories=dtype.categories)
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes([-2, 1, 2], dtype=dtype)

    def test_from_codes(self):
        dtype = CategoricalDtype(categories=["a", "b", "c"])
        exp = Categorical(["a", "b", "c"], ordered=False)
        res = Categorical.from_codes([0, 1, 2], categories=dtype.categories)
        tm.assert_categorical_equal(exp, res)

        res = Categorical.from_codes([0, 1, 2], dtype=dtype)
        tm.assert_categorical_equal(exp, res)

    @pytest.mark.parametrize("klass", [Categorical, CategoricalIndex])
    def test_from_codes_with_categorical_categories(self, klass):
        # GH17884
        expected = Categorical(["a", "b"], categories=["a", "b", "c"])

        result = Categorical.from_codes([0, 1], categories=klass(["a", "b", "c"]))
        tm.assert_categorical_equal(result, expected)

    @pytest.mark.parametrize("klass", [Categorical, CategoricalIndex])
    def test_from_codes_with_non_unique_categorical_categories(self, klass):
        with pytest.raises(ValueError, match="Categorical categories must be unique"):
            Categorical.from_codes([0, 1], klass(["a", "b", "a"]))

    def test_from_codes_with_nan_code(self):
        # GH21767
        codes = [1, 2, np.nan]
        dtype = CategoricalDtype(categories=["a", "b", "c"])
        with pytest.raises(ValueError, match="codes need to be array-like integers"):
            Categorical.from_codes(codes, categories=dtype.categories)
        with pytest.raises(ValueError, match="codes need to be array-like integers"):
            Categorical.from_codes(codes, dtype=dtype)

    @pytest.mark.parametrize("codes", [[1.0, 2.0, 0], [1.1, 2.0, 0]])
    def test_from_codes_with_float(self, codes):
        # GH21767
        # float codes should raise even if values are equal to integers
        dtype = CategoricalDtype(categories=["a", "b", "c"])

        msg = "codes need to be array-like integers"
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes(codes, dtype.categories)
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes(codes, dtype=dtype)

    def test_from_codes_with_dtype_raises(self):
        msg = "Cannot specify"
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes(
                [0, 1], categories=["a", "b"], dtype=CategoricalDtype(["a", "b"])
            )

        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes(
                [0, 1], ordered=True, dtype=CategoricalDtype(["a", "b"])
            )

    def test_from_codes_neither(self):
        msg = "Both were None"
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes([0, 1])

    def test_from_codes_with_nullable_int(self):
        codes = pd.array([0, 1], dtype="Int64")
        categories = ["a", "b"]

        result = Categorical.from_codes(codes, categories=categories)
        expected = Categorical.from_codes(codes.to_numpy(int), categories=categories)

        tm.assert_categorical_equal(result, expected)

    def test_from_codes_with_nullable_int_na_raises(self):
        codes = pd.array([0, None], dtype="Int64")
        categories = ["a", "b"]

        msg = "codes cannot contain NA values"
        with pytest.raises(ValueError, match=msg):
            Categorical.from_codes(codes, categories=categories)

    @pytest.mark.parametrize("dtype", [None, "category"])
    def test_from_inferred_categories(self, dtype):
        cats = ["a", "b"]
        codes = np.array([0, 0, 1, 1], dtype="i8")
        result = Categorical._from_inferred_categories(cats, codes, dtype)
        expected = Categorical.from_codes(codes, cats)
        tm.assert_categorical_equal(result, expected)

    @pytest.mark.parametrize("dtype", [None, "category"])
    def test_from_inferred_categories_sorts(self, dtype):
        cats = ["b", "a"]
        codes = np.array([0, 1, 1, 1], dtype="i8")
        result = Categorical._from_inferred_categories(cats, codes, dtype)
        expected = Categorical.from_codes([1, 0, 0, 0], ["a", "b"])
        tm.assert_categorical_equal(result, expected)

    def test_from_inferred_categories_dtype(self):
        cats = ["a", "b", "d"]
        codes = np.array([0, 1, 0, 2], dtype="i8")
        dtype = CategoricalDtype(["c", "b", "a"], ordered=True)
        result = Categorical._from_inferred_categories(cats, codes, dtype)
        expected = Categorical(
            ["a", "b", "a", "d"], categories=["c", "b", "a"], ordered=True
        )
        tm.assert_categorical_equal(result, expected)

    def test_from_inferred_categories_coerces(self):
        cats = ["1", "2", "bad"]
        codes = np.array([0, 0, 1, 2], dtype="i8")
        dtype = CategoricalDtype([1, 2])
        result = Categorical._from_inferred_categories(cats, codes, dtype)
        expected = Categorical([1, 1, 2, np.nan])
        tm.assert_categorical_equal(result, expected)

    @pytest.mark.parametrize("ordered", [None, True, False])
    def test_construction_with_ordered(self, ordered):
        # GH 9347, 9190
        cat = Categorical([0, 1, 2], ordered=ordered)
        assert cat.ordered == bool(ordered)

    @pytest.mark.xfail(reason="Imaginary values not supported in Categorical")
    def test_constructor_imaginary(self):
        values = [1, 2, 3 + 1j]
        c1 = Categorical(values)
        tm.assert_index_equal(c1.categories, Index(values))
        tm.assert_numpy_array_equal(np.array(c1), np.array(values))

    @pytest.mark.skipif(_np_version_under1p16, reason="Skipping for NumPy <1.16")
    def test_constructor_string_and_tuples(self):
        # GH 21416
        c = pd.Categorical(np.array(["c", ("a", "b"), ("b", "a"), "c"], dtype=object))
        expected_index = pd.Index([("a", "b"), ("b", "a"), "c"])
        assert c.categories.equals(expected_index)