BUG: Series.nlargest thinks True < False

doc/source/whatsnew/v0.25.0.rst

@@ -402,6 +402,7 @@ Reshaping
 - Bug in :func:`merge` where merging with equivalent Categorical dtypes was raising an error (:issue:`22501`)
 - Bug in :class:`DataFrame` constructor when passing non-empty tuples would cause a segmentation fault (:issue:`25691`)
 - Bug in :func:`pandas.cut` where large bins could incorrectly raise an error due to an integer overflow (:issue:`26045`)
+- Bug in :meth:`Series.nlargest` treats ``True`` as smaller than ``False`` (:issue:`26154`)
 
 Sparse
 ^^^^^^
@@ -415,7 +416,6 @@ Other
 ^^^^^
 
 -
--
 
 
 .. _whatsnew_0.250.contributors:

pandas/core/algorithms.py

@@ -1118,6 +1118,10 @@ def compute(self, method):
                 # GH 21426: ensure reverse ordering at boundaries
                 arr -= 1
 
+            elif is_bool_dtype(pandas_dtype):
+                # GH 26154: ensure False is smaller than True
+                arr = 1 - (-arr)
+
         if self.keep == 'last':
             arr = arr[::-1]
 

pandas/tests/series/test_analytics.py

@@ -1330,6 +1330,16 @@ def test_duplicate_keep_all_ties(self):
         expected = Series([6, 7, 7, 7, 7], index=[7, 3, 4, 5, 6])
         assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize('data,expected',
+                             [([True, False], [True]),
+                              ([True, False, True, True], [True])])
+    def test_boolean(self, data, expected):
+        # GH 26154 : ensure True > False
+        s = Series(data)
+        result = s.nlargest(1)
+        expected = Series(expected)
+        assert_series_equal(result, expected)
+
 
 class TestCategoricalSeriesAnalytics: