BUG-24971 copying blocks also considers ndim

doc/source/whatsnew/v0.24.2.rst

@@ -66,7 +66,7 @@ Bug Fixes
 
 **Categorical**
 
--
+- Bug where calling :meth:`Series.replace` on categorical data could return a ``Series`` with incorrect dimensions (:issue:`24971`)
 -
 -
 

pandas/core/internals/blocks.py

@@ -738,7 +738,7 @@ def copy(self, deep=True):
         values = self.values
         if deep:
             values = values.copy()
-        return self.make_block_same_class(values)
+        return self.make_block_same_class(values, ndim=self.ndim)
 
     def replace(self, to_replace, value, inplace=False, filter=None,
                 regex=False, convert=True):

pandas/tests/series/test_replace.py

@@ -280,3 +280,17 @@ def test_replace_mixed_types_with_string(self):
         result = s.replace([2, '4'], np.nan)
         expected = pd.Series([1, np.nan, 3, np.nan, 4, 5])
         tm.assert_series_equal(expected, result)
+
+    @pytest.mark.parametrize("categorical, numeric", [
+        (pd.Categorical('A', categories=['A', 'B']), [1]),
+        (pd.Categorical(('A', ), categories=['A', 'B']), [1]),
+        (pd.Categorical(('A', 'B'), categories=['A', 'B']), [1, 2]),
+    ])
+    def test_copy_categorical_ndim(self, categorical, numeric):
+        # GH 24971
+        s = pd.Series(categorical)
+        result = s.replace({'A': 1, 'B': 2})
+        expected = pd.Series(numeric)
+        print(result.dtype)
+        print(expected.dtype)
+        tm.assert_series_equal(expected, result, check_dtype=False)