Fix performance regression in ColumnTransformer #29330
Merged
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Fixes #29229
#28822 was a quick fix for #28781 before releasing 1.5.0. It turns out that it caused a performance regression when the input can't be memory mapped, for instance columns where elements are arrays of variable length. In that case the whole
X
is copied in each subprocess.Since #29018 has now been merged, we can revert #28822 because it also fixes #28781 without causing the performance regression (note that I kept the non regression test). The following results of the snippet from #29229 with this PR are close to the 1.4.2 ones: