Updated return val and test cases

Author: WillAyd

pandas/core/indexes/base.py

@@ -1878,14 +1878,7 @@ def get_duplicates(self):
                       "idx[idx.duplicated()].unique() instead",
                       FutureWarning, stacklevel=2)
 
-        return self._get_duplicates()
-
-    def _get_duplicates(self):
-        from collections import defaultdict
-        counter = defaultdict(lambda: 0)
-        for k in self.values:
-            counter[k] += 1
-        return sorted(k for k, v in compat.iteritems(counter) if v > 1)
+        return self[self.duplicated()].unique()
 
     def _cleanup(self):
         self._engine.clear_mapping()

pandas/tests/indexes/test_multi.py

@@ -2413,7 +2413,8 @@ def check(nlevels, with_nulls):
         for a in [101, 102]:
             mi = MultiIndex.from_arrays([[101, a], [3.5, np.nan]])
             assert not mi.has_duplicates
-            assert mi.get_duplicates() == []
+            assert mi.get_duplicates().equals(
+                MultiIndex.from_arrays([[], []]))
             tm.assert_numpy_array_equal(mi.duplicated(), np.zeros(
                 2, dtype='bool'))
 
@@ -2425,7 +2426,8 @@ def check(nlevels, with_nulls):
                                 labels=np.random.permutation(list(lab)).T)
                 assert len(mi) == (n + 1) * (m + 1)
                 assert not mi.has_duplicates
-                assert mi.get_duplicates() == []
+                assert mi.get_duplicates().equals(
+                    MultiIndex.from_arrays([[], []]))
                 tm.assert_numpy_array_equal(mi.duplicated(), np.zeros(
                     len(mi), dtype='bool'))