BUG: EA-backed boolean indexers

Closes #22665
Closes #22326

Author: TomAugspurger

doc/source/whatsnew/v0.24.0.txt

@@ -484,6 +484,7 @@ ExtensionType Changes
 - ``ExtensionArray`` has gained the abstract methods ``.dropna()`` (:issue:`21185`)
 - ``ExtensionDtype`` has gained the ability to instantiate from string dtypes, e.g. ``decimal`` would instantiate a registered ``DecimalDtype``; furthermore
   the ``ExtensionDtype`` has gained the method ``construct_array_type`` (:issue:`21185`)
+- An ``ExtensionArray`` with a boolean dtype now works correctly as a boolean indexer. :meth:`pandas.api.types.is_bool_dtype` now properly considers them boolean (:issue:`22326`)
 - Added ``ExtensionDtype._is_numeric`` for controlling whether an extension dtype is considered numeric (:issue:`22290`).
 - The ``ExtensionArray`` constructor, ``_from_sequence`` now take the keyword arg ``copy=False`` (:issue:`21185`)
 - Bug in :meth:`Series.get` for ``Series`` using ``ExtensionArray`` and integer index (:issue:`21257`)
@@ -608,6 +609,7 @@ Categorical
 ^^^^^^^^^^^
 
 - Bug in :meth:`Categorical.from_codes` where ``NaN`` values in ``codes`` were silently converted to ``0`` (:issue:`21767`). In the future this will raise a ``ValueError``. Also changes the behavior of ``.from_codes([1.1, 2.0])``.
+- Bug when indexing with a boolean-valued ``Categorical``. Now categoricals are treated as a boolean mask (:issue:`22665`)
 
 Datetimelike
 ^^^^^^^^^^^^

pandas/core/common.py

@@ -15,7 +15,9 @@
 from pandas import compat
 from pandas.compat import iteritems, PY36, OrderedDict
 from pandas.core.dtypes.generic import ABCSeries, ABCIndex, ABCIndexClass
-from pandas.core.dtypes.common import is_integer
+from pandas.core.dtypes.common import (
+    is_integer, is_bool_dtype, is_extension_array_dtype, is_array_like
+)
 from pandas.core.dtypes.inference import _iterable_not_string
 from pandas.core.dtypes.missing import isna, isnull, notnull  # noqa
 from pandas.core.dtypes.cast import construct_1d_object_array_from_listlike
@@ -100,7 +102,8 @@ def maybe_box_datetimelike(value):
 
 
 def is_bool_indexer(key):
-    if isinstance(key, (ABCSeries, np.ndarray, ABCIndex)):
+    if (isinstance(key, (ABCSeries, np.ndarray, ABCIndex)) or
+            (is_array_like(key) and is_extension_array_dtype(key.dtype))):
         if key.dtype == np.object_:
             key = np.asarray(values_from_object(key))
 
@@ -110,7 +113,7 @@ def is_bool_indexer(key):
                                      'NA / NaN values')
                 return False
             return True
-        elif key.dtype == np.bool_:
+        elif is_bool_dtype(key.dtype):
             return True
     elif isinstance(key, list):
         try:

pandas/core/dtypes/common.py

@@ -1608,6 +1608,8 @@ def is_bool_dtype(arr_or_dtype):
     False
     >>> is_bool_dtype(np.array([True, False]))
     True
+    >>> is_bool_dtype(pd.Categorical([True, False]))
+    True
     """
 
     if arr_or_dtype is None:
@@ -1618,6 +1620,13 @@ def is_bool_dtype(arr_or_dtype):
         # this isn't even a dtype
         return False
 
+    if isinstance(arr_or_dtype, (ABCCategorical, ABCCategoricalIndex)):
+        arr_or_dtype = arr_or_dtype.dtype
+
+    if isinstance(arr_or_dtype, CategoricalDtype):
+        arr_or_dtype = arr_or_dtype.categories
+        # now we use the special definition for Index
+
     if isinstance(arr_or_dtype, ABCIndexClass):
 
         # TODO(jreback)
@@ -1626,6 +1635,9 @@ def is_bool_dtype(arr_or_dtype):
         # guess this
         return (arr_or_dtype.is_object and
                 arr_or_dtype.inferred_type == 'boolean')
+    elif is_extension_array_dtype(arr_or_dtype):
+        dtype = getattr(arr_or_dtype, 'dtype', arr_or_dtype)
+        return issubclass(dtype.type, np.bool_)
 
     return issubclass(tipo, np.bool_)
 

pandas/tests/arrays/categorical/test_indexing.py

@@ -5,7 +5,8 @@
 import numpy as np
 
 import pandas.util.testing as tm
-from pandas import Categorical, Index, CategoricalIndex, PeriodIndex
+from pandas import Categorical, Index, CategoricalIndex, PeriodIndex, Series
+from pandas.core.common import is_bool_indexer
 from pandas.tests.arrays.categorical.common import TestCategorical
 
 
@@ -121,3 +122,12 @@ def test_get_indexer_non_unique(self, idx_values, key_values, key_class):
 
             tm.assert_numpy_array_equal(expected, result)
             tm.assert_numpy_array_equal(exp_miss, res_miss)
+
+
+def test_mask_with_boolean():
+    s = Series(range(3))
+    idx = CategoricalIndex([True, False, True])
+    assert is_bool_indexer(idx)
+    result = s[idx]
+    expected = s[idx.astype('object')]
+    tm.assert_series_equal(result, expected)