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BUG: ngroups and len(groups) do not equal when grouping with a list of Grouper and column label (GH26326) #26374

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Merged
merged 20 commits into from
May 20, 2019
Merged

BUG: ngroups and len(groups) do not equal when grouping with a list of Grouper and column label (GH26326) #26374

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47a1057
BUG: ngroups and len(groups) do not equal when grouping with a list o…
shantanu-gontia May 13, 2019
cad3d6b
Sorted Imports in test_groupby.py
shantanu-gontia May 13, 2019
0dba40d
Updated test and edited bugfix message
shantanu-gontia May 13, 2019
bb3f6de
Merge remote-tracking branch 'upstream/master' into bug26326
shantanu-gontia May 13, 2019
dc76a2d
Merge remote-tracking branch 'upstream/master' into bug26326
shantanu-gontia May 14, 2019
648ddfa
Updated method to not check for subclasses
shantanu-gontia May 14, 2019
3aaa15c
Merge remote-tracking branch 'upstream/master' into bug26326
shantanu-gontia May 14, 2019
f8a3220
fixed under indent on line 264
shantanu-gontia May 14, 2019
ca6eff6
Updated release file
shantanu-gontia May 16, 2019
c3d5de2
Merge branch 'master' into bug26326
shantanu-gontia May 16, 2019
f8f3d8f
patched solution with modification of BaseGrouper
shantanu-gontia May 16, 2019
b8e4b34
updated whatsnew file with better wording
shantanu-gontia May 16, 2019
bfdea4c
fixed whatsnew release note message
shantanu-gontia May 16, 2019
49615db
added issue number to message
shantanu-gontia May 16, 2019
050fb89
fixed linting
shantanu-gontia May 16, 2019
bf48c41
Merge branch 'master' into bug26326
shantanu-gontia May 19, 2019
af63e6e
fixed release note msg
shantanu-gontia May 19, 2019
fe0405a
Added test message, refactor test code
shantanu-gontia May 19, 2019
ee4dffe
remove extraneous function
shantanu-gontia May 19, 2019
ea023de
update release note msg
shantanu-gontia May 19, 2019
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2 changes: 1 addition & 1 deletion doc/source/whatsnew/v0.25.0.rst
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Expand Up @@ -406,7 +406,7 @@ Groupby/Resample/Rolling
- Bug in :meth:`pandas.core.groupby.GroupBy.idxmax` and :meth:`pandas.core.groupby.GroupBy.idxmin` with datetime column would return incorrect dtype (:issue:`25444`, :issue:`15306`)
- Bug in :meth:`pandas.core.groupby.GroupBy.cumsum`, :meth:`pandas.core.groupby.GroupBy.cumprod`, :meth:`pandas.core.groupby.GroupBy.cummin` and :meth:`pandas.core.groupby.GroupBy.cummax` with categorical column having absent categories, would return incorrect result or segfault (:issue:`16771`)
- Bug in :meth:`pandas.core.groupby.GroupBy.nth` where NA values in the grouping would return incorrect results (:issue:`26011`)

- Bug in :meth:`pandas.core.groupby.ops.BaseGrouper.groups` in which a :class:`BaseGrouper` object with another :class:`BaseGrouper` as part of its :class:`Groupings` would return incorrect set of groups (:issue:`26326`)
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Can you construct a message that is more user facing? These items aren't part of the API

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User facing as in more user friendly?


Reshaping
^^^^^^^^^
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5 changes: 4 additions & 1 deletion pandas/core/groupby/ops.py
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Expand Up @@ -258,7 +258,10 @@ def groups(self):
if len(self.groupings) == 1:
return self.groupings[0].groups
else:
to_groupby = zip(*(ping.grouper for ping in self.groupings))
to_groupby = zip(*(ping.grouper if not isinstance(ping.grouper,
self.__class__)
else ping.grouper.groupings[0].grouper for ping
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Wouldn't this only work if the grouper was the first item? Would need something more generalizable

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I was wondering the same. Can Groupers be nested to more than one level?

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I think this would fail if your test was .groupby(['beta', pd.Grouper(level='alpha')]) instead of .groupby([pd.Grouper(level='alpha'), 'beta'])

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@shantanu-gontia shantanu-gontia May 13, 2019 •
edited
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The problem is with the construction of the Groupings. The [0] indexes the sole BaseGrouper created inside the grouping due to the _get_grouper method. The order will be maintained. I have added another assertion to check this and it passed.

in self.groupings))
to_groupby = Index(to_groupby)
return self.axis.groupby(to_groupby)

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12 changes: 12 additions & 0 deletions pandas/tests/groupby/test_groupby.py
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Expand Up @@ -1737,3 +1737,15 @@ def test_groupby_multiindex_series_keys_len_equal_group_axis():
expected = pd.Series([3], index=ei)

assert_series_equal(result, expected)


def test_groupby_groups_in_BaseGrouper():
# https://github.com/pandas-dev/pandas/issues/26326
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Suggested change
# https://github.com/pandas-dev/pandas/issues/26326
# GH 26326

m_index = pd.MultiIndex.from_product([['A', 'B'],
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Use mi instead of m_index

['C', 'D']], names=['alpha', 'beta'])
df_sample = pd.DataFrame({'foo': [1, 2, 1, 2], 'bar': [1, 2, 3, 4]},
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df instead of df_sample

index=m_index)
dfGBY_BaseGrouper = df_sample.groupby([pd.Grouper(level='alpha'), 'beta'])
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Maybe just grp1 and grp2 for better readability here and line below

dfGBY_noBaseGrouper = df_sample.groupby(['alpha', 'beta'])

assert(dfGBY_BaseGrouper.groups == dfGBY_noBaseGrouper.groups)