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No SettingWithCopyWarning on groupby results #19152

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No SettingWithCopyWarning on groupby results #19152

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.23.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -425,6 +425,7 @@ Groupby/Resample/Rolling

- Bug when grouping by a single column and aggregating with a class like ``list`` or ``tuple`` (:issue:`18079`)
- Fixed regression in :func:`DataFrame.groupby` which would not emit an error when called with a tuple key not in the index (:issue:`18798`)
- Modifying a group dataframe while generating ``groupby`` results does not trigger a ``SettingWithCopyWarning`` (:issue:`19151`)
-
-

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4 changes: 3 additions & 1 deletion pandas/core/groupby.py
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Expand Up @@ -4722,7 +4722,9 @@ def __iter__(self):
# if start >= end:
# raise AssertionError('Start %s must be less than end %s'
# % (str(start), str(end)))
yield i, self._chop(sdata, slice(start, end))
group_data = self._chop(sdata, slice(start, end))
group_data._is_copy = None
yield i, group_data

def _get_sorted_data(self):
return self.data._take(self.sort_idx, axis=self.axis, convert=False)
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6 changes: 6 additions & 0 deletions pandas/tests/groupby/test_groupby.py
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Expand Up @@ -2758,6 +2758,12 @@ def test_tuple_correct_keyerror(self):
with tm.assert_raises_regex(KeyError, "(7, 8)"):
df.groupby((7, 8)).mean()

def test_no_setting_with_copy_warning(self):
df = pd.DataFrame({'x': range(4), 'c': list('aabb')})
for _, gdf in df.groupby('c'):
with tm.assert_produces_warning(None):
gdf['x'] = 1


def _check_groupby(df, result, keys, field, f=lambda x: x.sum()):
tups = lmap(tuple, df[keys].values)
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