API: Index.duplicated should return np.array

doc/source/whatsnew/v0.16.0.txt

@@ -27,6 +27,8 @@ Backwards incompatible API changes
 
 .. _whatsnew_0160.api_breaking:
 
+- ``Index.duplicated`` now returns `np.array(dtype=bool)` rathar than `Index(dtype=object)` containing `bool` values. (:issue:`8875`)
+
 Deprecations
 ~~~~~~~~~~~~
 

pandas/core/base.py

@@ -13,7 +13,8 @@
 
 
 _shared_docs = dict()
-_indexops_doc_kwargs = dict(klass='IndexOpsMixin', inplace='')
+_indexops_doc_kwargs = dict(klass='IndexOpsMixin', inplace='',
+                            duplicated='IndexOpsMixin')
 
 
 class StringMixin(object):
@@ -486,14 +487,14 @@ def searchsorted(self, key, side='left'):
     @Appender(_shared_docs['drop_duplicates'] % _indexops_doc_kwargs)
     def drop_duplicates(self, take_last=False, inplace=False):
         duplicated = self.duplicated(take_last=take_last)
-        result = self[~(duplicated.values).astype(bool)]
+        result = self[np.logical_not(duplicated)]
         if inplace:
             return self._update_inplace(result)
         else:
             return result
 
     _shared_docs['duplicated'] = (
-        """Return boolean %(klass)s denoting duplicate values
+        """Return boolean %(duplicated)s denoting duplicate values
 
         Parameters
         ----------
@@ -502,7 +503,7 @@ def drop_duplicates(self, take_last=False, inplace=False):
 
         Returns
         -------
-        duplicated : %(klass)s
+        duplicated : %(duplicated)s
         """)
 
     @Appender(_shared_docs['duplicated'] % _indexops_doc_kwargs)
@@ -513,8 +514,7 @@ def duplicated(self, take_last=False):
             return self._constructor(duplicated,
                                      index=self.index).__finalize__(self)
         except AttributeError:
-            from pandas.core.index import Index
-            return Index(duplicated)
+            return np.array(duplicated, dtype=bool)
 
     #----------------------------------------------------------------------
     # abstracts

pandas/core/index.py

@@ -33,7 +33,8 @@
 
 _unsortable_types = frozenset(('mixed', 'mixed-integer'))
 
-_index_doc_kwargs = dict(klass='Index', inplace='')
+_index_doc_kwargs = dict(klass='Index', inplace='',
+                         duplicated='np.array')
 
 
 def _try_get_item(x):

pandas/core/series.py

@@ -59,7 +59,8 @@
     klass='Series',
     axes_single_arg="{0,'index'}",
     inplace="""inplace : boolean, default False
-            If True, performs operation inplace and returns None."""
+            If True, performs operation inplace and returns None.""",
+    duplicated='Series'
 )
 
 

pandas/tests/test_base.py

@@ -614,8 +614,10 @@ def test_duplicated_drop_duplicates(self):
                     continue
 
                 # original doesn't have duplicates
-                expected = Index([False] * len(original))
-                tm.assert_index_equal(original.duplicated(), expected)
+                expected = np.array([False] * len(original), dtype=bool)
+                duplicated = original.duplicated()
+                tm.assert_numpy_array_equal(duplicated, expected)
+                self.assertTrue(duplicated.dtype == bool)
                 result = original.drop_duplicates()
                 tm.assert_index_equal(result, original)
                 self.assertFalse(result is original)
@@ -625,15 +627,19 @@ def test_duplicated_drop_duplicates(self):
 
                 # create repeated values, 3rd and 5th values are duplicated
                 idx = original[list(range(len(original))) + [5, 3]]
-                expected = Index([False] * len(original) + [True, True])
-                tm.assert_index_equal(idx.duplicated(), expected)
+                expected = np.array([False] * len(original) + [True, True], dtype=bool)
+                duplicated = idx.duplicated()
+                tm.assert_numpy_array_equal(duplicated, expected)
+                self.assertTrue(duplicated.dtype == bool)
                 tm.assert_index_equal(idx.drop_duplicates(), original)
 
                 last_base = [False] * len(idx)
                 last_base[3] = True
                 last_base[5] = True
-                expected = Index(last_base)
-                tm.assert_index_equal(idx.duplicated(take_last=True), expected)
+                expected = np.array(last_base)
+                duplicated = idx.duplicated(take_last=True)
+                tm.assert_numpy_array_equal(duplicated, expected)
+                self.assertTrue(duplicated.dtype == bool)
                 tm.assert_index_equal(idx.drop_duplicates(take_last=True),
                                       idx[~np.array(last_base)])
 

pandas/tests/test_multilevel.py

@@ -2075,13 +2075,17 @@ def test_duplicated_drop_duplicates(self):
         # GH 4060
         idx = MultiIndex.from_arrays(([1, 2, 3, 1, 2 ,3], [1, 1, 1, 1, 2, 2]))
 
-        expected = Index([False, False, False, True, False, False])
-        tm.assert_index_equal(idx.duplicated(), expected)
+        expected = np.array([False, False, False, True, False, False], dtype=bool)
+        duplicated = idx.duplicated()
+        tm.assert_numpy_array_equal(duplicated, expected)
+        self.assertTrue(duplicated.dtype == bool)
         expected = MultiIndex.from_arrays(([1, 2, 3, 2 ,3], [1, 1, 1, 2, 2]))
         tm.assert_index_equal(idx.drop_duplicates(), expected)
 
-        expected = Index([True, False, False, False, False, False])
-        tm.assert_index_equal(idx.duplicated(take_last=True), expected)
+        expected = np.array([True, False, False, False, False, False])
+        duplicated = idx.duplicated(take_last=True)
+        tm.assert_numpy_array_equal(duplicated, expected)
+        self.assertTrue(duplicated.dtype == bool)
         expected = MultiIndex.from_arrays(([2, 3, 1, 2 ,3], [1, 1, 1, 2, 2]))
         tm.assert_index_equal(idx.drop_duplicates(take_last=True), expected)