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REGR: Index.union loses python string dtype #54778

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Merged
merged 2 commits into from
Aug 28, 2023
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REGR: Index.union loses python string dtype #54778

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REGR: Index.union loses python string dtype
phofl Aug 27, 2023
4c5b735
Update pandas/core/indexes/base.py
phofl Aug 27, 2023
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2 changes: 1 addition & 1 deletion pandas/core/indexes/base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5194,7 +5194,7 @@ def _from_join_target(self, result: np.ndarray) -> ArrayLike:
"""
if isinstance(self.values, BaseMaskedArray):
return type(self.values)(result, np.zeros(result.shape, dtype=np.bool_))
elif isinstance(self.values, ArrowExtensionArray):
elif isinstance(self.values, (ArrowExtensionArray, StringArray)):
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just out of interest, why can't this be done for all EAs?

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We enhanced this when we added _get_join_target. Previously we returned result unchanged, so not sure if this would potentially break stuff

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ok - this looks fine to be, but would prefer if someone more familiar with core/indexes could take a look too

return type(self.values)._from_sequence(result)
return result

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7 changes: 7 additions & 0 deletions pandas/tests/indexes/test_setops.py
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Expand Up @@ -899,3 +899,10 @@ def test_union_ea_dtypes(self, any_numeric_ea_and_arrow_dtype):
result = idx.union(idx2)
expected = Index([1, 2, 3, 4, 5], dtype=any_numeric_ea_and_arrow_dtype)
tm.assert_index_equal(result, expected)

def test_union_string_array(self, any_string_dtype):
idx1 = Index(["a"], dtype=any_string_dtype)
idx2 = Index(["b"], dtype=any_string_dtype)
result = idx1.union(idx2)
expected = Index(["a", "b"], dtype=any_string_dtype)
tm.assert_index_equal(result, expected)