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BUG: Concat with inner join and empty DataFrame #15397

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BUG: Concat with inner join and empty DataFrame
abaldenko Feb 14, 2017
fc473b7
BUG: Concat with inner join and empty DataFrame
abaldenko Feb 14, 2017
47c8735
BUG: Concat with inner join and empty DataFrame
abaldenko Feb 16, 2017
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2 changes: 2 additions & 0 deletions doc/source/whatsnew/v0.20.0.txt
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Expand Up @@ -580,3 +580,5 @@ Bug Fixes
- Bug in ``Series.replace`` and ``DataFrame.replace`` which failed on empty replacement dicts (:issue:`15289`)
- Bug in ``pd.melt()`` where passing a tuple value for ``value_vars`` caused a ``TypeError`` (:issue:`15348`)
- Bug in ``.eval()`` which caused multiline evals to fail with local variables not on the first line (:issue:`15342`)
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just an FYI, if you put changes in whatsnew NOT at the end (but in empty space that is left), then you won't get conflicts.

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ah i see. makes sense. thanks!


- Bug in ``pd.concat()`` in which empty dataframe with ``join='inner'`` was being improperly handled (:issue:`15328`)
9 changes: 9 additions & 0 deletions pandas/tests/tools/test_concat.py
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Expand Up @@ -1825,6 +1825,15 @@ def test_concat_bug_3602(self):
result = concat([df1, df2], axis=1)
assert_frame_equal(result, expected)

def test_concat_bug_15328(self):
df_empty = pd.DataFrame()
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put a comment here for the issue number (rather than in the test name) (try to be descriptive with that if possible)

df_a = pd.DataFrame({'a': [1, 2]}, index=[0, 1])
result = pd.concat([df_empty, df_a], axis=1, join='inner')
self.assertTrue(result.empty)
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construct the result frame and use assert_frame_equal


result = pd.concat([df_a, df_empty], axis=1, join='inner')
self.assertTrue(result.empty)
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same


def test_concat_series_axis1_same_names_ignore_index(self):
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can you systematically tests the how=* here? (for the empty cases)

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sorry i'm not clear on what you mean here. could you clarify our point to something similar ?

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@jreback jreback Feb 14, 2017 •
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what I mean is something like:

for how, expected in [('inner', df_empty), ('outer', df_a), ('left', df_a), ('right', df_empty)]:
    result = pd.concat([df_a, df_empty, axis=1, join=how)
    assert_frame_equal(result, expected)

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oh haha. got it. thanks!

dates = date_range('01-Jan-2013', '01-Jan-2014', freq='MS')[0:-1]
s1 = Series(randn(len(dates)), index=dates, name='value')
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6 changes: 6 additions & 0 deletions pandas/tests/tools/test_merge.py
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Expand Up @@ -54,6 +54,12 @@ def setUp(self):
self.right = DataFrame({'v2': np.random.randn(4)},
index=['d', 'b', 'c', 'a'])

def test_merge_bug_15328(self):
df_empty = pd.DataFrame()
df_a = pd.DataFrame({'a': [1, 2]}, index=[0, 1])
result = pd.merge(df_empty, df_a, left_index=True, right_index=True)
self.assertTrue(result.empty)
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same as above


def test_merge_common(self):
joined = merge(self.df, self.df2)
exp = merge(self.df, self.df2, on=['key1', 'key2'])
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4 changes: 3 additions & 1 deletion pandas/tools/concat.py
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Expand Up @@ -284,7 +284,9 @@ def __init__(self, objs, axis=0, join='outer', join_axes=None,
if sum(obj.shape) > 0 or isinstance(obj, Series)]

if (len(non_empties) and (keys is None and names is None and
levels is None and join_axes is None)):
levels is None and
join_axes is None and
not self.intersect)):
objs = non_empties
sample = objs[0]

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