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BUG: MultiIndex.intersection duplicating nans in result #38984

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Merged
merged 7 commits into from
Jan 6, 2021
Merged

BUG: MultiIndex.intersection duplicating nans in result #38984

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0ffd4d0
Fix duplicates in MultiIndex.intersection with nan
phofl Dec 22, 2020
39cdaf3
Merge branch 'master' of https://github.com/pandas-dev/pandas into 38…
phofl Jan 6, 2021
0d52d03
Remove unused method
phofl Jan 6, 2021
dd92133
Add fixture and whatsnew
phofl Jan 6, 2021
c6ec54f
Refactor
phofl Jan 6, 2021
3ae707b
Refactor
phofl Jan 6, 2021
3d41d33
Merge branch 'master' of https://github.com/pandas-dev/pandas into 38623
phofl Jan 6, 2021
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v1.3.0.rst
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Expand Up @@ -260,6 +260,7 @@ MultiIndex
^^^^^^^^^^

- Bug in :meth:`DataFrame.drop` raising ``TypeError`` when :class:`MultiIndex` is non-unique and no level is provided (:issue:`36293`)
- Bug in :meth:`MultiIndex.intersection` duplicating ``NaN`` in result (:issue:`38623`)
- Bug in :meth:`MultiIndex.equals` incorrectly returning ``True`` when :class:`MultiIndex` containing ``NaN`` even when they are differntly ordered (:issue:`38439`)
- Bug in :meth:`MultiIndex.intersection` always returning empty when intersecting with :class:`CategoricalIndex` (:issue:`38653`)

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13 changes: 3 additions & 10 deletions pandas/core/indexes/multi.py
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Expand Up @@ -3578,16 +3578,9 @@ def _intersection(self, other, sort=False):
uniq_tuples = algos.unique(inner_tuples)

if uniq_tuples is None:
other_uniq = set(rvals)
seen = set()
# pandas\core\indexes\multi.py:3503: error: "add" of "set" does not
# return a value [func-returns-value]
uniq_tuples = [
x
for x in lvals
if x in other_uniq
and not (x in seen or seen.add(x)) # type: ignore[func-returns-value]
]
left_unique = self.drop_duplicates()
indexer = left_unique.get_indexer(other.drop_duplicates())
uniq_tuples = left_unique.take(np.sort(indexer[indexer != -1]))

if sort is None:
uniq_tuples = sorted(uniq_tuples)
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9 changes: 9 additions & 0 deletions pandas/tests/indexes/multi/test_setops.py
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Expand Up @@ -483,3 +483,12 @@ def test_intersection_different_names():
mi2 = MultiIndex.from_arrays([[1], [3]])
result = mi.intersection(mi2)
tm.assert_index_equal(result, mi2)


def test_intersection_with_missing_values_on_both_sides(nulls_fixture):
# GH#38623
mi1 = MultiIndex.from_arrays([[3, nulls_fixture, 4, nulls_fixture], [1, 2, 4, 2]])
mi2 = MultiIndex.from_arrays([[3, nulls_fixture, 3], [1, 2, 4]])
result = mi1.intersection(mi2)
expected = MultiIndex.from_arrays([[3.0, nulls_fixture], [1, 2]])
tm.assert_index_equal(result, expected)