# -*- coding: utf-8 -*-

from __future__ import print_function

import random

import numpy as np
import pytest

from pandas.compat import lrange

import pandas as pd
from pandas import (
    Categorical, DataFrame, IntervalIndex, MultiIndex, NaT, Series, Timestamp,
    date_range)
from pandas.api.types import CategoricalDtype
from pandas.tests.frame.common import TestData
import pandas.util.testing as tm
from pandas.util.testing import assert_frame_equal, assert_series_equal


class TestDataFrameSorting(TestData):

    def test_sort_values(self):
        frame = DataFrame([[1, 1, 2], [3, 1, 0], [4, 5, 6]],
                          index=[1, 2, 3], columns=list('ABC'))

        # by column (axis=0)
        sorted_df = frame.sort_values(by='A')
        indexer = frame['A'].argsort().values
        expected = frame.loc[frame.index[indexer]]
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.sort_values(by='A', ascending=False)
        indexer = indexer[::-1]
        expected = frame.loc[frame.index[indexer]]
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.sort_values(by='A', ascending=False)
        assert_frame_equal(sorted_df, expected)

        # GH4839
        sorted_df = frame.sort_values(by=['A'], ascending=[False])
        assert_frame_equal(sorted_df, expected)

        # multiple bys
        sorted_df = frame.sort_values(by=['B', 'C'])
        expected = frame.loc[[2, 1, 3]]
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.sort_values(by=['B', 'C'], ascending=False)
        assert_frame_equal(sorted_df, expected[::-1])

        sorted_df = frame.sort_values(by=['B', 'A'], ascending=[True, False])
        assert_frame_equal(sorted_df, expected)

        pytest.raises(ValueError, lambda: frame.sort_values(
            by=['A', 'B'], axis=2, inplace=True))

        # by row (axis=1): GH 10806
        sorted_df = frame.sort_values(by=3, axis=1)
        expected = frame
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.sort_values(by=3, axis=1, ascending=False)
        expected = frame.reindex(columns=['C', 'B', 'A'])
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.sort_values(by=[1, 2], axis='columns')
        expected = frame.reindex(columns=['B', 'A', 'C'])
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.sort_values(by=[1, 3], axis=1,
                                      ascending=[True, False])
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.sort_values(by=[1, 3], axis=1, ascending=False)
        expected = frame.reindex(columns=['C', 'B', 'A'])
        assert_frame_equal(sorted_df, expected)

        msg = r'Length of ascending \(5\) != length of by \(2\)'
        with pytest.raises(ValueError, match=msg):
            frame.sort_values(by=['A', 'B'], axis=0, ascending=[True] * 5)

    def test_sort_values_inplace(self):
        frame = DataFrame(np.random.randn(4, 4), index=[1, 2, 3, 4],
                          columns=['A', 'B', 'C', 'D'])

        sorted_df = frame.copy()
        sorted_df.sort_values(by='A', inplace=True)
        expected = frame.sort_values(by='A')
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.copy()
        sorted_df.sort_values(by=1, axis=1, inplace=True)
        expected = frame.sort_values(by=1, axis=1)
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.copy()
        sorted_df.sort_values(by='A', ascending=False, inplace=True)
        expected = frame.sort_values(by='A', ascending=False)
        assert_frame_equal(sorted_df, expected)

        sorted_df = frame.copy()
        sorted_df.sort_values(by=['A', 'B'], ascending=False, inplace=True)
        expected = frame.sort_values(by=['A', 'B'], ascending=False)
        assert_frame_equal(sorted_df, expected)

    def test_sort_nan(self):
        # GH3917
        nan = np.nan
        df = DataFrame({'A': [1, 2, nan, 1, 6, 8, 4],
                        'B': [9, nan, 5, 2, 5, 4, 5]})

        # sort one column only
        expected = DataFrame(
            {'A': [nan, 1, 1, 2, 4, 6, 8],
             'B': [5, 9, 2, nan, 5, 5, 4]},
            index=[2, 0, 3, 1, 6, 4, 5])
        sorted_df = df.sort_values(['A'], na_position='first')
        assert_frame_equal(sorted_df, expected)

        expected = DataFrame(
            {'A': [nan, 8, 6, 4, 2, 1, 1],
             'B': [5, 4, 5, 5, nan, 9, 2]},
            index=[2, 5, 4, 6, 1, 0, 3])
        sorted_df = df.sort_values(['A'], na_position='first', ascending=False)
        assert_frame_equal(sorted_df, expected)

        expected = df.reindex(columns=['B', 'A'])
        sorted_df = df.sort_values(by=1, axis=1, na_position='first')
        assert_frame_equal(sorted_df, expected)

        # na_position='last', order
        expected = DataFrame(
            {'A': [1, 1, 2, 4, 6, 8, nan],
             'B': [2, 9, nan, 5, 5, 4, 5]},
            index=[3, 0, 1, 6, 4, 5, 2])
        sorted_df = df.sort_values(['A', 'B'])
        assert_frame_equal(sorted_df, expected)

        # na_position='first', order
        expected = DataFrame(
            {'A': [nan, 1, 1, 2, 4, 6, 8],
             'B': [5, 2, 9, nan, 5, 5, 4]},
            index=[2, 3, 0, 1, 6, 4, 5])
        sorted_df = df.sort_values(['A', 'B'], na_position='first')
        assert_frame_equal(sorted_df, expected)

        # na_position='first', not order
        expected = DataFrame(
            {'A': [nan, 1, 1, 2, 4, 6, 8],
             'B': [5, 9, 2, nan, 5, 5, 4]},
            index=[2, 0, 3, 1, 6, 4, 5])
        sorted_df = df.sort_values(['A', 'B'], ascending=[
            1, 0], na_position='first')
        assert_frame_equal(sorted_df, expected)

        # na_position='last', not order
        expected = DataFrame(
            {'A': [8, 6, 4, 2, 1, 1, nan],
             'B': [4, 5, 5, nan, 2, 9, 5]},
            index=[5, 4, 6, 1, 3, 0, 2])
        sorted_df = df.sort_values(['A', 'B'], ascending=[
            0, 1], na_position='last')
        assert_frame_equal(sorted_df, expected)

        # Test DataFrame with nan label
        df = DataFrame({'A': [1, 2, nan, 1, 6, 8, 4],
                        'B': [9, nan, 5, 2, 5, 4, 5]},
                       index=[1, 2, 3, 4, 5, 6, nan])

        # NaN label, ascending=True, na_position='last'
        sorted_df = df.sort_index(
            kind='quicksort', ascending=True, na_position='last')
        expected = DataFrame({'A': [1, 2, nan, 1, 6, 8, 4],
                              'B': [9, nan, 5, 2, 5, 4, 5]},
                             index=[1, 2, 3, 4, 5, 6, nan])
        assert_frame_equal(sorted_df, expected)

        # NaN label, ascending=True, na_position='first'
        sorted_df = df.sort_index(na_position='first')
        expected = DataFrame({'A': [4, 1, 2, nan, 1, 6, 8],
                              'B': [5, 9, nan, 5, 2, 5, 4]},
                             index=[nan, 1, 2, 3, 4, 5, 6])
        assert_frame_equal(sorted_df, expected)

        # NaN label, ascending=False, na_position='last'
        sorted_df = df.sort_index(kind='quicksort', ascending=False)
        expected = DataFrame({'A': [8, 6, 1, nan, 2, 1, 4],
                              'B': [4, 5, 2, 5, nan, 9, 5]},
                             index=[6, 5, 4, 3, 2, 1, nan])
        assert_frame_equal(sorted_df, expected)

        # NaN label, ascending=False, na_position='first'
        sorted_df = df.sort_index(
            kind='quicksort', ascending=False, na_position='first')
        expected = DataFrame({'A': [4, 8, 6, 1, nan, 2, 1],
                              'B': [5, 4, 5, 2, 5, nan, 9]},
                             index=[nan, 6, 5, 4, 3, 2, 1])
        assert_frame_equal(sorted_df, expected)

    def test_stable_descending_sort(self):
        # GH #6399
        df = DataFrame([[2, 'first'], [2, 'second'], [1, 'a'], [1, 'b']],
                       columns=['sort_col', 'order'])
        sorted_df = df.sort_values(by='sort_col', kind='mergesort',
                                   ascending=False)
        assert_frame_equal(df, sorted_df)

    def test_stable_descending_multicolumn_sort(self):
        nan = np.nan
        df = DataFrame({'A': [1, 2, nan, 1, 6, 8, 4],
                        'B': [9, nan, 5, 2, 5, 4, 5]})
        # test stable mergesort
        expected = DataFrame(
            {'A': [nan, 8, 6, 4, 2, 1, 1],
             'B': [5, 4, 5, 5, nan, 2, 9]},
            index=[2, 5, 4, 6, 1, 3, 0])
        sorted_df = df.sort_values(['A', 'B'], ascending=[0, 1],
                                   na_position='first',
                                   kind='mergesort')
        assert_frame_equal(sorted_df, expected)

        expected = DataFrame(
            {'A': [nan, 8, 6, 4, 2, 1, 1],
             'B': [5, 4, 5, 5, nan, 9, 2]},
            index=[2, 5, 4, 6, 1, 0, 3])
        sorted_df = df.sort_values(['A', 'B'], ascending=[0, 0],
                                   na_position='first',
                                   kind='mergesort')
        assert_frame_equal(sorted_df, expected)

    def test_stable_categorial(self):
        # GH 16793
        df = DataFrame({
            'x': pd.Categorical(np.repeat([1, 2, 3, 4], 5), ordered=True)
        })
        expected = df.copy()
        sorted_df = df.sort_values('x', kind='mergesort')
        assert_frame_equal(sorted_df, expected)

    def test_sort_datetimes(self):

        # GH 3461, argsort / lexsort differences for a datetime column
        df = DataFrame(['a', 'a', 'a', 'b', 'c', 'd', 'e', 'f', 'g'],
                       columns=['A'],
                       index=date_range('20130101', periods=9))
        dts = [Timestamp(x)
               for x in ['2004-02-11', '2004-01-21', '2004-01-26',
                         '2005-09-20', '2010-10-04', '2009-05-12',
                         '2008-11-12', '2010-09-28', '2010-09-28']]
        df['B'] = dts[::2] + dts[1::2]
        df['C'] = 2.
        df['A1'] = 3.

        df1 = df.sort_values(by='A')
        df2 = df.sort_values(by=['A'])
        assert_frame_equal(df1, df2)

        df1 = df.sort_values(by='B')
        df2 = df.sort_values(by=['B'])
        assert_frame_equal(df1, df2)

        df1 = df.sort_values(by='B')

        df2 = df.sort_values(by=['C', 'B'])
        assert_frame_equal(df1, df2)

    def test_frame_column_inplace_sort_exception(self):
        s = self.frame['A']
        with pytest.raises(ValueError, match="This Series is a view"):
            s.sort_values(inplace=True)

        cp = s.copy()
        cp.sort_values()  # it works!

    def test_sort_nat_values_in_int_column(self):

        # GH 14922: "sorting with large float and multiple columns incorrect"

        # cause was that the int64 value NaT was considered as "na". Which is
        # only correct for datetime64 columns.

        int_values = (2, int(NaT))
        float_values = (2.0, -1.797693e308)

        df = DataFrame(dict(int=int_values, float=float_values),
                       columns=["int", "float"])

        df_reversed = DataFrame(dict(int=int_values[::-1],
                                     float=float_values[::-1]),
                                columns=["int", "float"],
                                index=[1, 0])

        # NaT is not a "na" for int64 columns, so na_position must not
        # influence the result:
        df_sorted = df.sort_values(["int", "float"], na_position="last")
        assert_frame_equal(df_sorted, df_reversed)

        df_sorted = df.sort_values(["int", "float"], na_position="first")
        assert_frame_equal(df_sorted, df_reversed)

        # reverse sorting order
        df_sorted = df.sort_values(["int", "float"], ascending=False)
        assert_frame_equal(df_sorted, df)

        # and now check if NaT is still considered as "na" for datetime64
        # columns:
        df = DataFrame(dict(datetime=[Timestamp("2016-01-01"), NaT],
                            float=float_values), columns=["datetime", "float"])

        df_reversed = DataFrame(dict(datetime=[NaT, Timestamp("2016-01-01")],
                                     float=float_values[::-1]),
                                columns=["datetime", "float"],
                                index=[1, 0])

        df_sorted = df.sort_values(["datetime", "float"], na_position="first")
        assert_frame_equal(df_sorted, df_reversed)

        df_sorted = df.sort_values(["datetime", "float"], na_position="last")
        assert_frame_equal(df_sorted, df)

        # Ascending should not affect the results.
        df_sorted = df.sort_values(["datetime", "float"], ascending=False)
        assert_frame_equal(df_sorted, df)

    def test_sort_nat(self):

        # GH 16836

        d1 = [Timestamp(x) for x in ['2016-01-01', '2015-01-01',
                                     np.nan, '2016-01-01']]
        d2 = [Timestamp(x) for x in ['2017-01-01', '2014-01-01',
                                     '2016-01-01', '2015-01-01']]
        df = pd.DataFrame({'a': d1, 'b': d2}, index=[0, 1, 2, 3])

        d3 = [Timestamp(x) for x in ['2015-01-01', '2016-01-01',
                                     '2016-01-01', np.nan]]
        d4 = [Timestamp(x) for x in ['2014-01-01', '2015-01-01',
                                     '2017-01-01', '2016-01-01']]
        expected = pd.DataFrame({'a': d3, 'b': d4}, index=[1, 3, 0, 2])
        sorted_df = df.sort_values(by=['a', 'b'], )
        tm.assert_frame_equal(sorted_df, expected)


class TestDataFrameSortIndexKinds(TestData):

    def test_sort_index_multicolumn(self):
        A = np.arange(5).repeat(20)
        B = np.tile(np.arange(5), 20)
        random.shuffle(A)
        random.shuffle(B)
        frame = DataFrame({'A': A, 'B': B,
                           'C': np.random.randn(100)})

        # use .sort_values #9816
        with tm.assert_produces_warning(FutureWarning):
            frame.sort_index(by=['A', 'B'])
        result = frame.sort_values(by=['A', 'B'])
        indexer = np.lexsort((frame['B'], frame['A']))
        expected = frame.take(indexer)
        assert_frame_equal(result, expected)

        # use .sort_values #9816
        with tm.assert_produces_warning(FutureWarning):
            frame.sort_index(by=['A', 'B'], ascending=False)
        result = frame.sort_values(by=['A', 'B'], ascending=False)
        indexer = np.lexsort((frame['B'].rank(ascending=False),
                              frame['A'].rank(ascending=False)))
        expected = frame.take(indexer)
        assert_frame_equal(result, expected)

        # use .sort_values #9816
        with tm.assert_produces_warning(FutureWarning):
            frame.sort_index(by=['B', 'A'])
        result = frame.sort_values(by=['B', 'A'])
        indexer = np.lexsort((frame['A'], frame['B']))
        expected = frame.take(indexer)
        assert_frame_equal(result, expected)

    def test_sort_index_inplace(self):
        frame = DataFrame(np.random.randn(4, 4), index=[1, 2, 3, 4],
                          columns=['A', 'B', 'C', 'D'])

        # axis=0
        unordered = frame.loc[[3, 2, 4, 1]]
        a_id = id(unordered['A'])
        df = unordered.copy()
        df.sort_index(inplace=True)
        expected = frame
        assert_frame_equal(df, expected)
        assert a_id != id(df['A'])

        df = unordered.copy()
        df.sort_index(ascending=False, inplace=True)
        expected = frame[::-1]
        assert_frame_equal(df, expected)

        # axis=1
        unordered = frame.loc[:, ['D', 'B', 'C', 'A']]
        df = unordered.copy()
        df.sort_index(axis=1, inplace=True)
        expected = frame
        assert_frame_equal(df, expected)

        df = unordered.copy()
        df.sort_index(axis=1, ascending=False, inplace=True)
        expected = frame.iloc[:, ::-1]
        assert_frame_equal(df, expected)

    def test_sort_index_different_sortorder(self):
        A = np.arange(20).repeat(5)
        B = np.tile(np.arange(5), 20)

        indexer = np.random.permutation(100)
        A = A.take(indexer)
        B = B.take(indexer)

        df = DataFrame({'A': A, 'B': B,
                        'C': np.random.randn(100)})

        # use .sort_values #9816
        with tm.assert_produces_warning(FutureWarning):
            df.sort_index(by=['A', 'B'], ascending=[1, 0])
        result = df.sort_values(by=['A', 'B'], ascending=[1, 0])

        ex_indexer = np.lexsort((df.B.max() - df.B, df.A))
        expected = df.take(ex_indexer)
        assert_frame_equal(result, expected)

        # test with multiindex, too
        idf = df.set_index(['A', 'B'])

        result = idf.sort_index(ascending=[1, 0])
        expected = idf.take(ex_indexer)
        assert_frame_equal(result, expected)

        # also, Series!
        result = idf['C'].sort_index(ascending=[1, 0])
        assert_series_equal(result, expected['C'])

    def test_sort_index_duplicates(self):

        # with 9816, these are all translated to .sort_values

        df = DataFrame([lrange(5, 9), lrange(4)],
                       columns=['a', 'a', 'b', 'b'])

        with pytest.raises(ValueError, match='not unique'):
            # use .sort_values #9816
            with tm.assert_produces_warning(FutureWarning):
                df.sort_index(by='a')
        with pytest.raises(ValueError, match='not unique'):
            df.sort_values(by='a')

        with pytest.raises(ValueError, match='not unique'):
            # use .sort_values #9816
            with tm.assert_produces_warning(FutureWarning):
                df.sort_index(by=['a'])
        with pytest.raises(ValueError, match='not unique'):
            df.sort_values(by=['a'])

        with pytest.raises(ValueError, match='not unique'):
            # use .sort_values #9816
            with tm.assert_produces_warning(FutureWarning):
                # multi-column 'by' is separate codepath
                df.sort_index(by=['a', 'b'])
        with pytest.raises(ValueError, match='not unique'):
            # multi-column 'by' is separate codepath
            df.sort_values(by=['a', 'b'])

        # with multi-index
        # GH4370
        df = DataFrame(np.random.randn(4, 2),
                       columns=MultiIndex.from_tuples([('a', 0), ('a', 1)]))
        with pytest.raises(ValueError, match='level'):
            # use .sort_values #9816
            with tm.assert_produces_warning(FutureWarning):
                df.sort_index(by='a')
        with pytest.raises(ValueError, match='level'):
            df.sort_values(by='a')

        # convert tuples to a list of tuples
        # use .sort_values #9816
        with tm.assert_produces_warning(FutureWarning):
            df.sort_index(by=[('a', 1)])
        expected = df.sort_values(by=[('a', 1)])

        # use .sort_values #9816
        with tm.assert_produces_warning(FutureWarning):
            df.sort_index(by=('a', 1))
        result = df.sort_values(by=('a', 1))
        assert_frame_equal(result, expected)

    def test_sort_index_level(self):
        mi = MultiIndex.from_tuples([[1, 1, 3], [1, 1, 1]], names=list('ABC'))
        df = DataFrame([[1, 2], [3, 4]], mi)
        res = df.sort_index(level='A', sort_remaining=False)
        assert_frame_equal(df, res)

        res = df.sort_index(level=['A', 'B'], sort_remaining=False)
        assert_frame_equal(df, res)

    def test_sort_index_categorical_index(self):

        df = (DataFrame({'A': np.arange(6, dtype='int64'),
                         'B': Series(list('aabbca'))
                        .astype(CategoricalDtype(list('cab')))})
              .set_index('B'))

        result = df.sort_index()
        expected = df.iloc[[4, 0, 1, 5, 2, 3]]
        assert_frame_equal(result, expected)

        result = df.sort_index(ascending=False)
        expected = df.iloc[[3, 2, 5, 1, 0, 4]]
        assert_frame_equal(result, expected)

    def test_sort_index(self):
        # GH13496

        frame = DataFrame(np.arange(16).reshape(4, 4), index=[1, 2, 3, 4],
                          columns=['A', 'B', 'C', 'D'])

        # axis=0 : sort rows by index labels
        unordered = frame.loc[[3, 2, 4, 1]]
        result = unordered.sort_index(axis=0)
        expected = frame
        assert_frame_equal(result, expected)

        result = unordered.sort_index(ascending=False)
        expected = frame[::-1]
        assert_frame_equal(result, expected)

        # axis=1 : sort columns by column names
        unordered = frame.iloc[:, [2, 1, 3, 0]]
        result = unordered.sort_index(axis=1)
        assert_frame_equal(result, frame)

        result = unordered.sort_index(axis=1, ascending=False)
        expected = frame.iloc[:, ::-1]
        assert_frame_equal(result, expected)

    @pytest.mark.parametrize("level", ['A', 0])  # GH 21052
    def test_sort_index_multiindex(self, level):
        # GH13496

        # sort rows by specified level of multi-index
        mi = MultiIndex.from_tuples([
            [2, 1, 3], [2, 1, 2], [1, 1, 1]], names=list('ABC'))
        df = DataFrame([[1, 2], [3, 4], [5, 6]], index=mi)

        expected_mi = MultiIndex.from_tuples([
            [1, 1, 1],
            [2, 1, 2],
            [2, 1, 3]], names=list('ABC'))
        expected = pd.DataFrame([
            [5, 6],
            [3, 4],
            [1, 2]], index=expected_mi)
        result = df.sort_index(level=level)
        assert_frame_equal(result, expected)

        # sort_remaining=False
        expected_mi = MultiIndex.from_tuples([
            [1, 1, 1],
            [2, 1, 3],
            [2, 1, 2]], names=list('ABC'))
        expected = pd.DataFrame([
            [5, 6],
            [1, 2],
            [3, 4]], index=expected_mi)
        result = df.sort_index(level=level, sort_remaining=False)
        assert_frame_equal(result, expected)

    def test_sort_index_intervalindex(self):
        # this is a de-facto sort via unstack
        # confirming that we sort in the order of the bins
        y = Series(np.random.randn(100))
        x1 = Series(np.sign(np.random.randn(100)))
        x2 = pd.cut(Series(np.random.randn(100)),
                    bins=[-3, -0.5, 0, 0.5, 3])
        model = pd.concat([y, x1, x2], axis=1, keys=['Y', 'X1', 'X2'])

        result = model.groupby(['X1', 'X2'], observed=True).mean().unstack()
        expected = IntervalIndex.from_tuples(
            [(-3.0, -0.5), (-0.5, 0.0),
             (0.0, 0.5), (0.5, 3.0)],
            closed='right')
        result = result.columns.levels[1].categories
        tm.assert_index_equal(result, expected)

    def test_sort_index_na_position_with_categories(self):
        # GH 22556
        # Positioning missing value properly when column is Categorical.
        categories = ['A', 'B', 'C']
        category_indices = [0, 2, 4]
        list_of_nans = [np.nan, np.nan]
        na_indices = [1, 3]
        na_position_first = 'first'
        na_position_last = 'last'
        column_name = 'c'

        reversed_categories = sorted(categories, reverse=True)
        reversed_category_indices = sorted(category_indices, reverse=True)
        reversed_na_indices = sorted(na_indices, reverse=True)

        df = pd.DataFrame({
            column_name: pd.Categorical(['A', np.nan, 'B', np.nan, 'C'],
                                        categories=categories,
                                        ordered=True)})
        # sort ascending with na first
        result = df.sort_values(by=column_name,
                                ascending=True,
                                na_position=na_position_first)
        expected = DataFrame({
            column_name: Categorical(list_of_nans + categories,
                                     categories=categories,
                                     ordered=True)
        }, index=na_indices + category_indices)

        assert_frame_equal(result, expected)

        # sort ascending with na last
        result = df.sort_values(by=column_name,
                                ascending=True,
                                na_position=na_position_last)
        expected = DataFrame({
            column_name: Categorical(categories + list_of_nans,
                                     categories=categories,
                                     ordered=True)
        }, index=category_indices + na_indices)

        assert_frame_equal(result, expected)

        # sort descending with na first
        result = df.sort_values(by=column_name,
                                ascending=False,
                                na_position=na_position_first)
        expected = DataFrame({
            column_name: Categorical(list_of_nans + reversed_categories,
                                     categories=categories,
                                     ordered=True)
        }, index=reversed_na_indices + reversed_category_indices)

        assert_frame_equal(result, expected)

        # sort descending with na last
        result = df.sort_values(by=column_name,
                                ascending=False,
                                na_position=na_position_last)
        expected = DataFrame({
            column_name: Categorical(reversed_categories + list_of_nans,
                                     categories=categories,
                                     ordered=True)
        }, index=reversed_category_indices + reversed_na_indices)

        assert_frame_equal(result, expected)

    def test_sort_index_na_position_with_categories_raises(self):
        df = pd.DataFrame({
            'c': pd.Categorical(['A', np.nan, 'B', np.nan, 'C'],
                                categories=['A', 'B', 'C'],
                                ordered=True)})

        with pytest.raises(ValueError):
            df.sort_values(by='c',
                           ascending=False,
                           na_position='bad_position')
