ERR: Make get_indexer return the correct indexer when Index is numeric and target is boolean (#16877)

Author: andrejonasson

doc/source/whatsnew/v0.21.0.txt

@@ -358,6 +358,7 @@ Indexing
 - Allow unicode empty strings as placeholders in multilevel columns in Python 2 (:issue:`17099`)
 - Bug in ``.iloc`` when used with inplace addition or assignment and an int indexer on a ``MultiIndex`` causing the wrong indexes to be read from and written to (:issue:`17148`)
 - Bug in ``.isin()`` in which checking membership in empty ``Series`` objects raised an error (:issue:`16991`)
+- When a numeric ``Index``'s :func:`get_indexer` is passed a boolean target it now returns the correct indexer  (:issue:`16877`)
 
 I/O
 ^^^

pandas/core/indexes/base.py

@@ -2584,6 +2584,9 @@ def get_indexer(self, target, method=None, limit=None, tolerance=None):
         if tolerance is not None:
             tolerance = self._convert_tolerance(tolerance)
 
+        if target.is_boolean() and self.is_numeric():
+            return np.repeat(-1, target.size)
+
         pself, ptarget = self._maybe_promote(target)
         if pself is not self or ptarget is not target:
             return pself.get_indexer(ptarget, method=method, limit=limit,
@@ -2612,7 +2615,6 @@ def get_indexer(self, target, method=None, limit=None, tolerance=None):
                                  'backfill or nearest reindexing')
 
             indexer = self._engine.get_indexer(target._values)
-
         return _ensure_platform_int(indexer)
 
     def _convert_tolerance(self, tolerance):

pandas/tests/indexes/test_base.py

@@ -1131,6 +1131,18 @@ def test_get_indexer_strings(self):
         with pytest.raises(TypeError):
             idx.get_indexer(['a', 'b', 'c', 'd'], method='pad', tolerance=2)
 
+    def test_get_indexer_boolean_index_boolean_target(self):
+        boolean_idx = pd.Index([True, False])
+        actual = boolean_idx.get_indexer([True, True, False])
+        expected = np.array([0, 0, 1])
+        tm.assert_numpy_array_equal(actual, expected, check_dtype=False)
+
+    def test_get_indexer_numeric_index_boolean_target(self):
+        numeric_idx = pd.Index(range(4))
+        actual = numeric_idx.get_indexer([True, False, True])
+        expected = np.repeat(-1, 3)
+        tm.assert_numpy_array_equal(actual, expected, check_dtype=False)
+
     def test_get_loc(self):
         idx = pd.Index([0, 1, 2])
         all_methods = [None, 'pad', 'backfill', 'nearest']