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Fix left join turning into outer join #19624

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Merged
merged 4 commits into from
Feb 10, 2018
Merged

Fix left join turning into outer join #19624

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01355d5
BUG: Fix 'left' join turned into 'outer' join when joining with a seq…
elrubio Feb 9, 2018
d1a85e4
TST: Check for correct index after left-joining a sequence of datafra…
elrubio Feb 9, 2018
6eb27ab
Test fixture removed, using assert_frame_equal
elrubio Feb 9, 2018
0a068a0
Mention bug in release notes
elrubio Feb 10, 2018
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13 changes: 6 additions & 7 deletions pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5328,18 +5328,17 @@ def _join_compat(self, other, on=None, how='left', lsuffix='', rsuffix='',
raise ValueError('Joining multiple DataFrames only supported'
' for joining on index')

# join indexes only using concat
if how == 'left':
how = 'outer'
join_axes = [self.index]
else:
join_axes = None

frames = [self] + list(other)

can_concat = all(df.index.is_unique for df in frames)

# join indexes only using concat
if can_concat:
if how == 'left':
how = 'outer'
join_axes = [self.index]
else:
join_axes = None
return concat(frames, axis=1, join=how, join_axes=join_axes,
verify_integrity=True)

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13 changes: 13 additions & 0 deletions pandas/tests/frame/test_join.py
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Expand Up @@ -31,6 +31,11 @@ def right():
return DataFrame({'b': [300, 100, 200]}, index=[3, 1, 2])


@pytest.fixture
def right_non_unique():
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Why'd you make this a fixture? If it's only used in one place then I'd prefer it be defined where it's used.

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Well, the below test is just the bare minimum, I think test_join needs to cover many more situations. But I will pull it into the method for now.

return DataFrame({'c': [400, 500, 600]}, index=[2, 2, 4])


@pytest.mark.parametrize(
"how, sort, expected",
[('inner', False, DataFrame({'a': [20, 10],
Expand Down Expand Up @@ -165,3 +170,11 @@ def test_join_period_index(frame_with_period_index):
index=frame_with_period_index.index)

tm.assert_frame_equal(joined, expected)


def test_join_left_sequence_non_unique_index(left, right, right_non_unique):
# left join sequence of dataframes with non-unique indices (issue #19607)
joined = left.join([right_non_unique], how='left')
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Could you also build the expected output and tm.assert_frame_equal against that?

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That should definitely be possible

tm.assert_index_equal(
joined.index.unique().sort_values(),
left.index.sort_values())