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BUG: Inconsistent behavior of Groupby with None values with filter (#… #63178

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BUG: Inconsistent behavior of Groupby with None values with filter (#… #63178

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v2.3.4.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ including other versions of pandas.
Bug fixes
^^^^^^^^^
- Bug in :meth:`DataFrame.__getitem__` returning modified columns when called with ``slice`` in Python 3.12 (:issue:`57500`)
- Fix bug in :meth:`~DataFrame.groupby` with ``None`` values with filter (:issue:`62501`)

.. ---------------------------------------------------------------------------
.. _whatsnew_234.contributors:
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10 changes: 9 additions & 1 deletion pandas/core/groupby/groupby.py
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Expand Up @@ -650,6 +650,8 @@ def get_converter(s):
return lambda key: Timestamp(key)
elif isinstance(s, np.datetime64):
return lambda key: Timestamp(key).asm8
elif isna(s):
return lambda key: np.nan
else:
return lambda key: key

Expand Down Expand Up @@ -684,11 +686,17 @@ def get_converter(s):
for name in names
)

elif any(isna(k) for k in self.indices.keys()):
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@rhshadrach rhshadrach Nov 23, 2025

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This check is expensive - this function is only ever called currently with names a list of length 1, and the rest of the method is O(1) in terms of self.indices. It's called from the inner loop of DataFramGroupBy.fitler as we're iterating over each group. This seems avoidable.

I believe we could change this function to just accept a single name (rather than a list) and then have a special case:

if isna(name):
    return self.indices.get(np.nan, [])

converters = [get_converter(name) for name in names]
names = (converter(name) for converter, name in zip(converters, names))

else:
converter = get_converter(index_sample)
names = (converter(name) for name in names)

return [self.indices.get(name, []) for name in names]
indices = {np.nan if isna(k) else k: v for k, v in self.indices.items()}
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@rhshadrach rhshadrach Nov 23, 2025

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It seems better to do this on indices cached property directly, and only in the case where there is a NaN value with if not self.dropna and self.result_index.hasnans.


return [indices.get(name, []) for name in names]

@final
def _get_index(self, name):
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