PERF: avoid copy in concatenate_array_managers if reindex already copies #44559
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jorisvandenbossche
added
ArrayManager
Performance
pandas/core/internals/concat.py
Outdated
| @@ -94,7 +99,7 @@ def _concatenate_array_managers( | |||
| # concatting along the columns -> combine reindexed arrays in a single manager | |||
| assert concat_axis == 0 | |||
| arrays = list(itertools.chain.from_iterable([mgr.arrays for mgr in mgrs])) | |||
| if copy: | |||
| if copy and axis1_needs_copy_this: | |||
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might be cleaner (and avoid copies in corner cases) to do this up in the for loop right before mgrs.append(mgr)
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Thanks, good idea, and that also simplified it quite a bit
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lgtm @jbrockmendel comment could be addressed here |
jbrockmendel
reviewed
Dec 4, 2021
pandas/core/internals/concat.py
Outdated
| @@ -77,10 +77,16 @@ def _concatenate_array_managers( | |||
| # reindex all arrays | |||
| mgrs = [] | |||
| for mgr, indexers in mgrs_indexers: | |||
| axis1_needs_copy = True | |||
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nitpick again: elsewhere in this file we do basically the same thing with made_copy = False
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@jbrockmendel #42797 added an unconditional copy, while if you reindex the arrays, you already are sure you have a copy.
This gives a 20% improvement on some of the merge benchmarks.