REF: share Index.difference (#38676)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -2906,8 +2906,13 @@ def difference(self, other, sort=None):
  other, result_name = self._convert_can_do_setop(other)
 
  if self.equals(other):
+ # Note: we do not (yet) sort even if sort=None GH#24959
  return self[:0].rename(result_name)
 
+ if len(other) == 0:
+ # Note: we do not (yet) sort even if sort=None GH#24959
+ return self.rename(result_name)
+
  result = self._difference(other, sort=sort)
  return self._wrap_setop_result(other, result)
 

pandas/core/indexes/multi.py

@@ -3676,42 +3676,9 @@ def _intersection(self, other, sort=False):
  zip(*uniq_tuples), sortorder=0, names=result_names
  )
 
- def difference(self, other, sort=None):
- """
- Compute set difference of two MultiIndex objects
-
- Parameters
- ----------
- other : MultiIndex
- sort : False or None, default None
- Sort the resulting MultiIndex if possible
-
- .. versionadded:: 0.24.0
-
- .. versionchanged:: 0.24.1
-
- Changed the default value from ``True`` to ``None``
- (without change in behaviour).
-
- Returns
- -------
- diff : MultiIndex
- """
- self._validate_sort_keyword(sort)
- self._assert_can_do_setop(other)
+ def _difference(self, other, sort):
  other, result_names = self._convert_can_do_setop(other)
 
- if len(other) == 0:
- return self.rename(result_names)
-
- if self.equals(other):
- return MultiIndex(
- levels=self.levels,
- codes=[[]] * self.nlevels,
- names=result_names,
- verify_integrity=False,
- )
-
  this = self._get_unique_index()
 
  indexer = this.get_indexer(other)

pandas/core/indexes/period.py

@@ -635,16 +635,6 @@ def _setop(self, other, sort, opname: str):
  def _intersection(self, other, sort=False):
  return self._setop(other, sort, opname="intersection")
 
- def difference(self, other, sort=None):
- self._validate_sort_keyword(sort)
- self._assert_can_do_setop(other)
- other, result_name = self._convert_can_do_setop(other)
-
- if self.equals(other):
- return self[:0].rename(result_name)
-
- return self._difference(other, sort=sort)
-
  def _difference(self, other, sort):
 
  if is_object_dtype(other):

pandas/tests/indexes/datetimes/test_setops.py

@@ -326,7 +326,8 @@ def test_difference(self, tz, sort):
  (rng3, other3, expected3),
  ]:
  result_diff = rng.difference(other, sort)
- if sort is None:
+ if sort is None and len(other):
+ # We dont sort (yet?) when empty GH#24959
  expected = expected.sort_values()
  tm.assert_index_equal(result_diff, expected)
 

pandas/tests/indexes/multi/test_setops.py

@@ -294,7 +294,9 @@ def test_intersection(idx, sort):
  # assert result.equals(tuples)
 
 
-@pytest.mark.parametrize("method", ["intersection", "union"])
+@pytest.mark.parametrize(
+ "method", ["intersection", "union", "difference", "symmetric_difference"]
+)
 def test_setop_with_categorical(idx, sort, method):
  other = idx.to_flat_index().astype("category")
  res_names = [None] * idx.nlevels

pandas/tests/indexes/period/test_setops.py

@@ -318,7 +318,8 @@ def test_difference(self, sort):
  (rng7, other7, expected7),
  ]:
  result_difference = rng.difference(other, sort=sort)
- if sort is None:
+ if sort is None and len(other):
+ # We dont sort (yet?) when empty GH#24959
  expected = expected.sort_values()
  tm.assert_index_equal(result_difference, expected)