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Backport PR #57034 on branch 2.2.x (REGR: perf regression in Series.combine_first) #57072

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Merged
merged 1 commit into from
Jan 25, 2024
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Backport PR #57034 on branch 2.2.x (REGR: perf regression in Series.combine_first) #57072

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v2.2.1.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ including other versions of pandas.

Fixed regressions
~~~~~~~~~~~~~~~~~
- Fixed performance regression in :meth:`Series.combine_first` (:issue:`55845`)
- Fixed regression in :func:`merge_ordered` raising ``TypeError`` for ``fill_method="ffill"`` and ``how="left"`` (:issue:`57010`)
- Fixed regression in :meth:`Series.pct_change` raising a ``ValueError`` for an empty :class:`Series` (:issue:`57056`)

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8 changes: 8 additions & 0 deletions pandas/core/series.py
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Expand Up @@ -86,6 +86,7 @@
from pandas.core.dtypes.dtypes import (
CategoricalDtype,
ExtensionDtype,
SparseDtype,
)
from pandas.core.dtypes.generic import (
ABCDataFrame,
Expand Down Expand Up @@ -3510,6 +3511,13 @@ def combine_first(self, other) -> Series:
"""
from pandas.core.reshape.concat import concat

if self.dtype == other.dtype:
if self.index.equals(other.index):
return self.mask(self.isna(), other)
elif self._can_hold_na and not isinstance(self.dtype, SparseDtype):
this, other = self.align(other, join="outer")
return this.mask(this.isna(), other)

new_index = self.index.union(other.index)

this = self
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