BUG: fix Series constructor for scalar and Categorical dtype (#19717)

Author: cbertinato

doc/source/whatsnew/v0.23.0.txt

@@ -730,7 +730,8 @@ Categorical
  ``self`` but in a different order (:issue:`19551`)
 - Bug in :meth:`Index.astype` with a categorical dtype where the resultant index is not converted to a :class:`CategoricalIndex` for all types of index (:issue:`18630`)
 - Bug in :meth:`Series.astype` and ``Categorical.astype()`` where an existing categorical data does not get updated (:issue:`10696`, :issue:`18593`)
-- Bug in :class:`Index` constructor with ``dtype=CategoricalDtype(...)`` where ``categories`` and ``ordered`` are not maintained (:issue:`19032`)
+- Bug in :class:`Index` constructor with ``dtype=CategoricalDtype(...)`` where ``categories`` and ``ordered`` are not maintained (issue:`19032`)
+- Bug in :class:`Series` constructor with scalar and ``dtype=CategoricalDtype(...)`` where ``categories`` and ``ordered`` are not maintained (issue:`19565`)
 
 Datetimelike
 ^^^^^^^^^^^^

pandas/core/dtypes/cast.py

@@ -1178,7 +1178,7 @@ def construct_1d_arraylike_from_scalar(value, length, dtype):
  subarr = DatetimeIndex([value] * length, dtype=dtype)
  elif is_categorical_dtype(dtype):
  from pandas import Categorical
- subarr = Categorical([value] * length)
+ subarr = Categorical([value] * length, dtype=dtype)
  else:
  if not isinstance(dtype, (np.dtype, type(np.dtype))):
  dtype = dtype.dtype

pandas/tests/dtypes/test_cast.py

@@ -22,7 +22,8 @@
  maybe_convert_string_to_object,
  maybe_convert_scalar,
  find_common_type,
- construct_1d_object_array_from_listlike)
+ construct_1d_object_array_from_listlike,
+ construct_1d_arraylike_from_scalar)
 from pandas.core.dtypes.dtypes import (
  CategoricalDtype,
  DatetimeTZDtype,
@@ -422,3 +423,15 @@ def test_cast_1d_array(self, datum1, datum2):
  @pytest.mark.parametrize('val', [1, 2., None])
  def test_cast_1d_array_invalid_scalar(self, val):
  pytest.raises(TypeError, construct_1d_object_array_from_listlike, val)
+
+ def test_cast_1d_arraylike_from_scalar_categorical(self):
+ # GH 19565 - Categorical result from scalar did not maintain categories
+ # and ordering of the passed dtype
+ cats = ['a', 'b', 'c']
+ cat_type = CategoricalDtype(categories=cats, ordered=False)
+ expected = pd.Categorical(['a', 'a'], categories=cats)
+ result = construct_1d_arraylike_from_scalar('a', len(expected),
+ cat_type)
+ tm.assert_categorical_equal(result, expected,
+ check_category_order=True,
+ check_dtype=True)

pandas/tests/series/test_constructors.py

@@ -270,6 +270,13 @@ def test_constructor_categorical_dtype(self):
  tm.assert_index_equal(result.cat.categories, pd.Index(['b', 'a']))
  assert result.cat.ordered is False
 
+ # GH 19565 - Check broadcasting of scalar with Categorical dtype
+ result = Series('a', index=[0, 1],
+ dtype=CategoricalDtype(['a', 'b'], ordered=True))
+ expected = Series(['a', 'a'], index=[0, 1],
+ dtype=CategoricalDtype(['a', 'b'], ordered=True))
+ tm.assert_series_equal(result, expected, check_categorical=True)
+
  def test_categorical_sideeffects_free(self):
  # Passing a categorical to a Series and then changing values in either
  # the series or the categorical should not change the values in the