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BUG/TST: TimeGrouper has erroneous groups if key length is too short #13028

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BUG/TST: TimeGrouper has erroneous groups if key length is too short #13028

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51 changes: 51 additions & 0 deletions pandas/tests/test_groupby.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4507,6 +4507,57 @@ def test_groupby_with_empty(self):
grouped = series.groupby(grouper)
assert next(iter(grouped), None) is None

def test_aaa_groupby_with_small_elem(self):
# GH 8542
# length=2
df = pd.DataFrame({'event': ['start', 'start'],
'change': [1234, 5678]},
index=pd.DatetimeIndex(['2014-09-10', '2013-10-10']))
grouped = df.groupby([pd.TimeGrouper(freq='M'), 'event'])
self.assertEqual(len(grouped.groups), 2)
self.assertEqual(grouped.ngroups, 2)
self.assertIn((pd.Timestamp('2014-09-30'), 'start'), grouped.groups)
self.assertIn((pd.Timestamp('2013-10-31'), 'start'), grouped.groups)

res = grouped.get_group((pd.Timestamp('2014-09-30'), 'start'))
tm.assert_frame_equal(res, df.iloc[[0], :])
res = grouped.get_group((pd.Timestamp('2013-10-31'), 'start'))
tm.assert_frame_equal(res, df.iloc[[1], :])

df = pd.DataFrame({'event': ['start', 'start', 'start'],
'change': [1234, 5678, 9123]},
index=pd.DatetimeIndex(['2014-09-10', '2013-10-10',
'2014-09-15']))
grouped = df.groupby([pd.TimeGrouper(freq='M'), 'event'])
self.assertEqual(len(grouped.groups), 2)
self.assertEqual(grouped.ngroups, 2)
self.assertIn((pd.Timestamp('2014-09-30'), 'start'), grouped.groups)
self.assertIn((pd.Timestamp('2013-10-31'), 'start'), grouped.groups)

res = grouped.get_group((pd.Timestamp('2014-09-30'), 'start'))
tm.assert_frame_equal(res, df.iloc[[0, 2], :])
res = grouped.get_group((pd.Timestamp('2013-10-31'), 'start'))
tm.assert_frame_equal(res, df.iloc[[1], :])

# length=3
df = pd.DataFrame({'event': ['start', 'start', 'start'],
'change': [1234, 5678, 9123]},
index=pd.DatetimeIndex(['2014-09-10', '2013-10-10',
'2014-08-05']))
grouped = df.groupby([pd.TimeGrouper(freq='M'), 'event'])
self.assertEqual(len(grouped.groups), 3)
self.assertEqual(grouped.ngroups, 3)
self.assertIn((pd.Timestamp('2014-09-30'), 'start'), grouped.groups)
self.assertIn((pd.Timestamp('2013-10-31'), 'start'), grouped.groups)
self.assertIn((pd.Timestamp('2014-08-31'), 'start'), grouped.groups)

res = grouped.get_group((pd.Timestamp('2014-09-30'), 'start'))
tm.assert_frame_equal(res, df.iloc[[0], :])
res = grouped.get_group((pd.Timestamp('2013-10-31'), 'start'))
tm.assert_frame_equal(res, df.iloc[[1], :])
res = grouped.get_group((pd.Timestamp('2014-08-31'), 'start'))
tm.assert_frame_equal(res, df.iloc[[2], :])

def test_groupby_with_timezone_selection(self):
# GH 11616
# Test that column selection returns output in correct timezone.
Expand Down