8000 Backport PR #44192 on branch 1.3.x (PERF: read_csv GH#44106) by meeseeksmachine · Pull Request #44197 · pandas-dev/pandas · GitHub
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Backport PR #44192 on branch 1.3.x (PERF: read_csv GH#44106) #44197

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Merged
merged 1 commit into from
Oct 27, 2021
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Backport PR #44192 on branch 1.3.x (PERF: read_csv GH#44106) #44197

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Backport PR #44192: PERF: read_csv GH#44106
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@jbrockmendel @meeseeksmachine
8000 jbrockmendel authored and meeseeksmachine committed Oct 26, 2021
commit 5f4d6683ba5c5ee1b38b9174b91369efc9be601a
2 changes: 1 addition & 1 deletion doc/source/whatsnew/v1.3.5.rst
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Expand Up @@ -14,7 +14,7 @@ including other versions of pandas.

Fixed regressions
~~~~~~~~~~~~~~~~~
-
- Fixed performance regression in :func:`read_csv` (:issue:`44106`)
-

.. ---------------------------------------------------------------------------
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89CB
7 changes: 4 additions & 3 deletions pandas/io/parsers/c_parser_wrapper.py
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Expand Up @@ -206,9 +206,10 @@ def _set_noconvert_columns(self):
"""
assert self.orig_names is not None
# error: Cannot determine type of 'names'
col_indices = [
self.orig_names.index(x) for x in self.names # type: ignore[has-type]
]

# much faster than using orig_names.index(x) xref GH#44106
names_dict = {x: i for i, x in enumerate(self.orig_names)}
col_indices = [names_dict[x] for x in self.names] # type: ignore[has-type]
# error: Cannot determine type of 'names'
noconvert_columns = self._set_noconvert_dtype_columns(
col_indices,
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0