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BUG: Bug in groupby .apply with a non-affecting mutation in the function (GH8467) #8484

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Merged
merged 1 commit into from
Oct 6, 2014
Merged

BUG: Bug in groupby .apply with a non-affecting mutation in the function (GH8467) #8484

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2 changes: 1 addition & 1 deletion doc/source/v0.15.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -946,7 +946,7 @@ Bug Fixes
- Bug in ``is_superperiod`` and ``is_subperiod`` cannot handle higher frequencies than ``S`` (:issue:`7760`, :issue:`7772`, :issue:`7803`)
- Bug in 32-bit platforms with ``Series.shift`` (:issue:`8129`)
- Bug in ``PeriodIndex.unique`` returns int64 ``np.ndarray`` (:issue:`7540`)

- Bug in groupby ``.apply`` with a non-affecting mutation in the function (:issue:`8467`)
- Bug in ``DataFrame.reset_index`` which has ``MultiIndex`` contains ``PeriodIndex`` or ``DatetimeIndex`` with tz raises ``ValueError`` (:issue:`7746`, :issue:`7793`)


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3 changes: 2 additions & 1 deletion pandas/core/groupby.py
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Expand Up @@ -2851,8 +2851,9 @@ def _wrap_applied_output(self, keys, values, not_indexed_same=False):
return concat(values)

if not all_indexed_same:
# GH 8467
return self._concat_objects(
keys, values, not_indexed_same=not_indexed_same
keys, values, not_indexed_same=True,
)

try:
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12 changes: 12 additions & 0 deletions pandas/tests/test_groupby.py
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Expand Up @@ -2112,6 +2112,18 @@ def f_no_copy(x):
grpby_no_copy = mydf.groupby('cat1').apply(f_no_copy)
assert_series_equal(grpby_copy,grpby_no_copy)

def test_no_mutate_but_looks_like(self):

# GH 8467
# first show's mutation indicator
# second does not, but should yield the same results
df = DataFrame({'key': [1, 1, 1, 2, 2, 2, 3, 3, 3],
'value': range(9)})

result1 = df.groupby('key', group_keys=True).apply(lambda x: x[:].key)
result2 = df.groupby('key', group_keys=True).apply(lambda x: x.key)
assert_series_equal(result1, result2)

def test_apply_chunk_view(self):
# Low level tinkering could be unsafe, make sure not
df = DataFrame({'key': [1, 1, 1, 2, 2, 2, 3, 3, 3],
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