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BUG: Allow concat to take string axis names #14389

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BUG: Allow concat to take string axis names #14389

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584ebd2
BUG: Allow concat to take string axis names
brandonmburroughs Oct 10, 2016
a6694b9
Updating documentation
brandonmburroughs Oct 10, 2016
cf3f998
Adding ValueError test for concat Series axis 'columns'
brandonmburroughs Oct 11, 2016
3f08b07
Adding concat tests for axis 0, 1, and 'index'
brandonmburroughs Oct 12, 2016
fdd5260
Removing duplicate expected dfs
brandonmburroughs Oct 12, 2016
64702fb
Updating documentation for concat
brandonmburroughs Oct 12, 2016
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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.19.1.txt
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Expand Up @@ -44,4 +44,5 @@ Bug Fixes


- Bug in ``pd.concat`` where names of the ``keys`` were not propagated to the resulting ``MultiIndex`` (:issue:`14252`)
- Bug in ``pd.concat`` where ``axis`` cannot take string parameters ``rows`` or ``columns (:issue:`14369`)
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missing closing backticks after "columns"
Small other thing: I would also quote the parameters inside the backticks (like 'rows' ) to make clear it are string arguments

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Good idea. Added!

- Bug in ``MultiIndex.set_levels`` where illegal level values were still set after raising an error (:issue:`13754`)
14 changes: 14 additions & 0 deletions pandas/tests/frame/test_combine_concat.py
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Expand Up @@ -347,6 +347,20 @@ def test_concat_named_keys(self):
names=[None, None]))
assert_frame_equal(concatted_unnamed, expected_unnamed)

def test_concat_axis_parameter(self):
# GH 14369
df1 = pd.DataFrame({'A': [0.1, 0.2]}, index=range(2))
df2 = pd.DataFrame({'A': [0.3, 0.4]}, index=range(2))
expected_row = pd.DataFrame(
{'A': [0.1, 0.2, 0.3, 0.4]}, index=[0, 1, 0, 1])
concatted_row = pd.concat([df1, df2], axis='rows')
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Probably already tested elsewhere, but can you add for completeness in this test also the index=0 case and check output of that as well? (and the same for axis=1 below)

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What does this mean? I looked through the concat parameters (as well as some other tests) and didn't see index=0. Do you mean joining dataframes without indices?

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Whoops, sorry, I meant axis=0 in addition to axis='index'

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Okay, that makes sense! Tests added.

assert_frame_equal(concatted_row, expected_row)

expected_columns = pd.DataFrame(
[[0.1, 0.3], [0.2, 0.4]], index=[0, 1], columns=['A', 'A'])
concatted_columns = pd.concat([df1, df2], axis='columns')
assert_frame_equal(concatted_columns, expected_columns)


class TestDataFrameCombineFirst(tm.TestCase, TestData):

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6 changes: 5 additions & 1 deletion pandas/tools/merge.py
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Expand Up @@ -1283,7 +1283,7 @@ def concat(objs, axis=0, join='outer', join_axes=None, ignore_index=False,
argument, unless it is passed, in which case the values will be
selected (see below). Any None objects will be dropped silently unless
they are all None in which case a ValueError will be raised
axis : {0, 1, ...}, default 0
axis : {0, 1, 'rows', 'columns', ...}, default 0
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Can you make this something like {0/'index', 1/'columns'} to make it clear which are equivalent?

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Yes, that makes sense. Done.

The axis to concatenate along
join : {'inner', 'outer'}, default 'outer'
How to handle indexes on other axis(es)
Expand Down Expand Up @@ -1411,6 +1411,10 @@ def __init__(self, objs, axis=0, join='outer', join_axes=None,
sample = objs[0]
self.objs = objs

# Check for string axis parameter
if isinstance(axis, str):
axis = objs[0]._get_axis_number(axis)
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This will not work in case of concatting different Serieses with axis='columns', as this axis is not defined for Series

Can you also add a test for such case?

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@jreback Does there already exist a utility function similar to _get_axis_number that does not depend on the actual object?

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I've added the test. Thanks for pointing that out!

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What I wanted to say is that the code will not work in that case, but I think it should work (which means that we cannot use _get_axis_number ..)
I am not sure there is already some functionality that does this for you, so you will have to mimic what is in _get_axis_numbers. You maybe can use DataFrame._AXIS_NUMBERS/NAMES

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iirc it's a class method so something like

NDFrame._get_axis_number(axis) should work

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That would have been indeed have been useful, but it is not a class method .. (the attributes like _AXIS_NAMES are also only defined in the subclasses). And I don't think we have this logic already somewhere else (as in other methods you can just used the instance method)

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Yeah, axis='columns' should work since axis=1 works for a Series. Unfortunately NDFrame._get_axis_number(axis) isn't a class method.

I've added a function in pandas.tools.util that emulates get_axis_number (in fact, it's mostly the same). I wasn't sure where to put this, but this function uses DataFrame._AXIS_NUMBERS/NAMES. This won't depend on specific objects and allows concat of Series to work with both columns (new functionality) and 1 (works in 0.19.0). I've updated existing tests and added new ones for the util function.

Does this work? It allows axis='columns' to be used for two Series though it gets all of the axis names from DataFrame.


# Need to flip BlockManager axis in the DataFrame special case
self._is_frame = isinstance(sample, DataFrame)
if self._is_frame:
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