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Improve performance when selecting rows and columns #53014

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Merged
merged 4 commits into from
May 4, 2023
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Merged

Improve performance when selecting rows and columns #53014

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7f77219
Improve performance when selecting rows and columns
phofl Apr 30, 2023
82a011d
Update doc/source/whatsnew/v2.1.0.rst
phofl May 2, 2023
abe96eb
Update indexing.py
phofl May 2, 2023
01c9eab
Update v2.1.0.rst
phofl May 3, 2023
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v2.1.0.rst
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Expand Up @@ -283,6 +283,7 @@ Performance improvements
- Performance improvement accessing :attr:`arrays.IntegerArrays.dtype` & :attr:`arrays.FloatingArray.dtype` (:issue:`52998`)
- Performance improvement in :class:`Series` reductions (:issue:`52341`)
- Performance improvement in :func:`concat` when ``axis=1`` and objects have different indexes (:issue:`52541`)
- Performance improvement in :meth:`DataFrame.loc` when selecting rows and columns (:issue:`53014`)
- Performance improvement in :meth:`Series.corr` and :meth:`Series.cov` for extension dtypes (:issue:`52502`)
- Performance improvement in :meth:`Series.to_numpy` when dtype is a numpy float dtype and ``na_value`` is ``np.nan`` (:issue:`52430`)
- Performance improvement in :meth:`~arrays.ArrowExtensionArray.to_numpy` (:issue:`52525`)
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4 changes: 3 additions & 1 deletion pandas/core/indexing.py
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Expand Up @@ -933,7 +933,9 @@ def _getitem_tuple_same_dim(self, tup: tuple):
This is only called after a failed call to _getitem_lowerdim.
"""
retval = self.obj
for i, key in enumerate(tup):
# Selecting columns before rows is signficiantly faster
for i, key in enumerate(reversed(tup)):
i = self.ndim - i - 1
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Comment about why doing it this way, otherwise future-me might try to “simplify” it

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Can also put this right before retval = ...

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Added a comment, prefer keeping it here. We might miss this if we use i before this at some point

if com.is_null_slice(key):
continue

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