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BUG in .groupby for single-row DF #12063

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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v0.18.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -497,7 +497,7 @@ Bug Fixes
of columns didn't match the number of series provided (:issue:`12039`).



- Bug in ``.groupby`` where a ``KeyError`` was not raised for a wrong column if there was only one row in the dataframe (:issue:`11741`)


- Removed ``millisecond`` property of ``DatetimeIndex``. This would always raise a ``ValueError`` (:issue:`12019`).
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3 changes: 2 additions & 1 deletion pandas/core/groupby.py
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Expand Up @@ -2207,11 +2207,12 @@ def _get_grouper(obj, key=None, axis=0, level=None, sort=True):

if not isinstance(key, (tuple, list)):
keys = [key]
match_axis_length = False
else:
keys = key
match_axis_length = len(keys) == len(group_axis)

# what are we after, exactly?
match_axis_length = len(keys) == len(group_axis)
any_callable = any(callable(g) or isinstance(g, dict) for g in keys)
any_groupers = any(isinstance(g, Grouper) for g in keys)
any_arraylike = any(isinstance(g, (list, tuple, Series, Index, np.ndarray))
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7 changes: 7 additions & 0 deletions pandas/tests/test_groupby.py
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Expand Up @@ -3085,6 +3085,13 @@ def test_groupby_keys_same_size_as_index(self):

assert_frame_equal(result, expected)

def test_groupby_one_row(self):
# GH 11741
df1 = pd.DataFrame(np.random.randn(1, 4), columns=list('ABCD'))
self.assertRaises(KeyError, df1.groupby, 'Z')
df2 = pd.DataFrame(np.random.randn(2, 4), columns=list('ABCD'))
self.assertRaises(KeyError, df2.groupby, 'Z')

def test_groupby_nat_exclude(self):
# GH 6992
df = pd.DataFrame({'values': np.random.randn(8),
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