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BUG: Index.difference not always returning a unique set of values #55113

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merged 5 commits into from
Sep 18, 2023
Merged

BUG: Index.difference not always returning a unique set of values #55113

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8f3c1ee
BUG: Index.difference not always returning a unique set of values
lukemanley Sep 12, 2023
3a568ed
whatsnew
lukemanley Sep 12, 2023
097d428
Merge remote-tracking branch 'upstream/main' into bug-index-differenc…
lukemanley Sep 13, 2023
ab11566
udpate test
lukemanley Sep 13, 2023
8d6a07f
update test
lukemanley Sep 13, 2023
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v2.2.0.rst
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Expand Up @@ -231,7 +231,7 @@ Interval

Indexing
^^^^^^^^
-
- Bug in :meth:`Index.difference` not returning a unique set of values when ``other`` is empty or ``other`` is considered non-comparable (:issue:`55113`)
-

Missing
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4 changes: 2 additions & 2 deletions pandas/core/indexes/base.py
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Expand Up @@ -3598,14 +3598,14 @@ def difference(self, other, sort=None):

if len(other) == 0:
# Note: we do not (yet) sort even if sort=None GH#24959
result = self.rename(result_name)
result = self.unique().rename(result_name)
if sort is True:
return result.sort_values()
return result

if not self._should_compare(other):
# Nothing matches -> difference is everything
result = self.rename(result_name)
result = self.unique().rename(result_name)
if sort is True:
return result.sort_values()
return result
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10 changes: 9 additions & 1 deletion pandas/tests/indexes/test_setops.py
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Expand Up @@ -799,8 +799,16 @@ def test_difference_empty_arg(self, index, sort):
first = index[5:20]
first.name = "name"
result = first.difference([], sort)
expected = first.unique()
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Could you construct a completely new Index for `expected instead (and below)?

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Updated

tm.assert_index_equal(result, expected)

tm.assert_index_equal(result, first)
def test_difference_should_not_compare(self):
# GH 55113
left = Index([1, 1])
right = Index([True])
result = left.difference(right)
expected = left.unique()
tm.assert_index_equal(result, expected)

@pytest.mark.parametrize("index", ["string"], indirect=True)
def test_difference_identity(self, index, sort):
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