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PERF: Try fast/slow paths only once in DataFrameGroupby.transform #42195

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Merged
merged 8 commits into from
Jul 8, 2021
Merged

PERF: Try fast/slow paths only once in DataFrameGroupby.transform #42195

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7b86fdb
PERF: Try fast/slow paths only once in DataFrameGroupby.transform
rhshadrach Jun 23, 2021
b70e420
Avoid checking path each iteration
rhshadrach Jun 23, 2021
15d238a
fix
rhshadrach Jun 23, 2021
36de30e
Make process_result return instead of mutate
rhshadrach Jul 7, 2021
2c1d337
Merge branch 'master' of https://github.com/pandas-dev/pandas into gr…
rhshadrach Jul 7, 2021
2d40eaa
whatsnew
rhshadrach Jul 7, 2021
ec9515b
Comment, refactor, and narrow typing
rhshadrach Jul 7, 2021
2bea964
r -> res_frame
rhshadrach Jul 8, 2021
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20 changes: 12 additions & 8 deletions pandas/core/groupby/generic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1309,17 +1309,21 @@ def _transform_general(self, func, *args, **kwargs):
gen = self.grouper.get_iterator(obj, axis=self.axis)
fast_path, slow_path = self._define_paths(func, *args, **kwargs)

path = None
for name, group in gen:
object.__setattr__(group, "name", name)

# Try slow path and fast path.
try:
path, res = self._choose_path(fast_path, slow_path, group)
except TypeError:
return self._transform_item_by_item(obj, fast_path)
except ValueError as err:
msg = "transform must return a scalar value for each group"
raise ValueError(msg) from err
if path is None:
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instead of doing this at each step in the loop, can we just do this outside the loop?

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Yes - updated PR to show what this would look like. Minor cleanups can be done to avoid the nested if statements in the newly added process_result, but it's a bit ugly. We're trading if path is None for a function call as I don't see another way to avoid code duplication.

# Try slow path and fast path.
try:
path, res = self._choose_path(fast_path, slow_path, group)
except TypeError:
return self._transform_item_by_item(obj, fast_path)
except ValueError as err:
msg = "transform must return a scalar value for each group"
raise ValueError(msg) from err
else:
res = path(group)

if isinstance(res, Series):

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