PERF: Use DataFrame-level reductions in DataFrame.agg with list of funcs#65031
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When DataFrame.agg receives a list of function names (e.g. ["sum"]), use DataFrame-level reductions per dtype group instead of extracting each column as a Series and calling Series.agg per column. closes pandas-dev#45658 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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cc @rhshadrach |
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Apr 10, 2026
| # Compute reductions per dtype group to preserve per-column dtypes. | ||
| # Using to_frame().T for each result avoids the slow | ||
| # DataFrame(list-of-Series) construction path. | ||
| groups = obj.columns.groupby(obj.dtypes) # type: ignore[arg-type] |
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I like this - but do you feel certain that we can rely on equality of dtypes here? I don't know of any examples that would cause problems, just wondering if there are edge cases where dtypes would give as equal when there is some subtle difference (e.g. time resolution).
As long as it's the case that if two dtypes say they are equal when they are not precisely equal we would call this a bug, I'm good here.
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We can't prevent a hypothetical 3rd party EADtype from lying about its equality, but im pretty confident this works as expected for all our dtypes.
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Thanks @jbrockmendel |
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…-comparison * upstream/main: PERF: use lookup instead of hash_inner_join for merge with unique right keys (pandas-dev#64691) BUG : update `SeriesGroupBy.ohlc()` to honor `as_index=False` (pandas-dev#65141) PERF: Use DataFrame-level reductions in DataFrame.agg with list of funcs (pandas-dev#65031) DOC: document required external libraries in read_* I/O docstrings (pandas-dev#65143) DOC: improve MultiIndex.is_monotonic_increasing/decreasing docstrings (pandas-dev#65154) BUG: Raise ValueError for non-boolean numeric_only in DataFrame/Series reductions (GH#53098) (pandas-dev#65131) BUG: Timedelta.round() raises ZeroDivisionError when internal unit is 's' and target frequency is sub-second (pandas-dev#64836) ENH: Add replace method to Index (closes pandas-dev#19495) (pandas-dev#65099) PERF: improve StringArray.isna (pandas-dev#57733) BUG: read parquet files with older pytz (DEP: keep lower pytz minimum version) (pandas-dev#65133) DEPR: deprecate dates-with-datetime64 in _maybe_downcast_for_indexing (pandas-dev#64871) DOC: note that DataFrame.values is not writeable (pandas-dev#65142) CLN: Update groupby observed defaults (pandas-dev#65148) PERF: avoid materializing values[indexer] in Block.setitem (pandas-dev#64251) DOC: update GroupBy.sum/min/max See Also sections (pandas-dev#65144)
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Summary
DataFrame.aggreceives a list of string function names (e.g.["sum", "mean"]), use DataFrame-level reductions per dtype group instead of extracting each column as a Series and callingSeries.aggper column.df.agg(["sum"])from ~110ms to ~0.5ms (~220x speedup).closes #45658
Test plan
pandas/tests/apply/tests pass (922 passed)pandas/tests/reductions/tests pass (546 passed)🤖 Generated with Claude Code