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REGR/PERF: Fix perf regression in _LocationIndexer._post_expansion_casting #64388

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Merged
mroeschke merged 3 commits into from
Mar 6, 2026
+8 −8
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REGR/PERF: Fix perf regression in _LocationIndexer._post_expansion_casting #64388

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REGR/PERF: Fix performance regression in _LocationIndexer._post_expan…
rhshadrach Mar 3, 2026
9c67ed5
Use _mgr.get_dtypes
rhshadrach Mar 4, 2026
45a7036
Use flatnonzero
rhshadrach Mar 6, 2026
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16 changes: 8 additions & 8 deletions pandas/core/indexing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -955,14 +955,14 @@ def _post_expansion_casting(self, orig_obj) -> None:
self.obj._mgr = new_ser._mgr
elif orig_obj.shape[1] == self.obj.shape[1]:
# We added rows but not columns
for i in range(orig_obj.shape[1]):
new_dtype = self.obj.dtypes.iloc[i]
orig_dtype = orig_obj.dtypes.iloc[i]
if new_dtype != orig_dtype:
new_arr = infer_and_maybe_downcast(
orig_obj.iloc[:, i].array, self.obj.iloc[:, i]._values
)
self.obj.isetitem(i, new_arr)
changed_dtypes = (
self.obj._mgr.get_dtypes() != orig_obj._mgr.get_dtypes()
)
for i in np.flatnonzero(changed_dtypes):
new_arr = infer_and_maybe_downcast(
orig_obj.iloc[:, i].array, self.obj.iloc[:, i]._values
)
self.obj.isetitem(i, new_arr)

elif orig_obj.columns.is_unique and self.obj.columns.is_unique:
for col in orig_obj.columns:
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