BUG: Avoid duplicates in DatetimeIndex.intersection (#38196)

Author: phofl

pandas/core/indexes/datetimelike.py

@@ -689,6 +689,8 @@ def intersection(self, other, sort=False):
  other, _ = self._convert_can_do_setop(other)
 
  if self.equals(other):
+ if self.has_duplicates:
+ return self.unique()._get_reconciled_name_object(other)
  return self._get_reconciled_name_object(other)
 
  return self._intersection(other, sort=sort)

pandas/tests/indexes/datetimes/test_setops.py

@@ -510,6 +510,20 @@ def test_month_range_union_tz_dateutil(self, sort):
 
  early_dr.union(late_dr, sort=sort)
 
+ @pytest.mark.parametrize("sort", [False, None])
+ def test_intersection_duplicates(self, sort):
+ # GH#38196
+ idx1 = Index(
+ [
+ pd.Timestamp("2019-12-13"),
+ pd.Timestamp("2019-12-12"),
+ pd.Timestamp("2019-12-12"),
+ ]
+ )
+ result = idx1.intersection(idx1, sort=sort)
+ expected = Index([pd.Timestamp("2019-12-13"), pd.Timestamp("2019-12-12")])
+ tm.assert_index_equal(result, expected)
+
 
 class TestCustomDatetimeIndex:
  def setup_method(self, method):