test_categorical.py 文件源码

def test_shift(self):
        # GH 9416
        cat = pd.Categorical(['a', 'b', 'c', 'd', 'a'])

        # shift forward
        sp1 = cat.shift(1)
        xp1 = pd.Categorical([np.nan, 'a', 'b', 'c', 'd'])
        self.assert_categorical_equal(sp1, xp1)
        self.assert_categorical_equal(cat[:-1], sp1[1:])

        # shift back
        sn2 = cat.shift(-2)
        xp2 = pd.Categorical(['c', 'd', 'a', np.nan, np.nan],
                             categories=['a', 'b', 'c', 'd'])
        self.assert_categorical_equal(sn2, xp2)
        self.assert_categorical_equal(cat[2:], sn2[:-2])

        # shift by zero
        self.assert_categorical_equal(cat, cat.shift(0))