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REGR: Performance of DataFrame.stack where columns are not a MultiIndex #58027

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merged 1 commit into from
Mar 27, 2024
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REGR: Performance of DataFrame.stack where columns are not a MultiIndex #58027

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20 changes: 12 additions & 8 deletions pandas/core/reshape/reshape.py
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Original file line number Diff line number Diff line change
Expand Up @@ -932,14 +932,18 @@ def stack_v3(frame: DataFrame, level: list[int]) -> Series | DataFrame:
if len(frame.columns) == 1:
data = frame.copy()
else:
# Take the data from frame corresponding to this idx value
if len(level) == 1:
idx = (idx,)
gen = iter(idx)
column_indexer = tuple(
next(gen) if k in set_levels else slice(None)
for k in range(frame.columns.nlevels)
)
if not isinstance(frame.columns, MultiIndex) and not isinstance(idx, tuple):
# GH#57750 - if the frame is an Index with tuples, .loc below will fail
column_indexer = idx
else:
# Take the data from frame corresponding to this idx value
if len(level) == 1:
idx = (idx,)
gen = iter(idx)
column_indexer = tuple(
next(gen) if k in set_levels else slice(None)
for k in range(frame.columns.nlevels)
)
data = frame.loc[:, column_indexer]

if len(level) < frame.columns.nlevels:
Expand Down