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BUG: Fix index order for Index.intersection() #15583

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BUG: Fix index order for Index.intersection() #15583

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c12bb3f
BUG: Fix index order for Index.intersection()
Mar 5, 2017
c2a8dc3
Implement tests
Mar 6, 2017
a4ead99
Fix typo
Mar 6, 2017
e7bcd28
Fix typo in documentation
Mar 8, 2017
d9e29f8
Create new DatetimeIndex from the Index.intersection result
Mar 8, 2017
1197b99
Fix DataFrame column order when read from HDF file
Mar 12, 2017
784fe75
Fix error: line too long
Mar 12, 2017
b977278
Address requested changes
Mar 14, 2017
ec836bd
Fix Travis errors
Mar 15, 2017
047b513
Address requested changes
Mar 15, 2017
c96306d
Add sort argument to Index.join
Mar 15, 2017
f0d9d03
Add whatsnew
Mar 15, 2017
ef2581e
Fix Travis error
Mar 15, 2017
3c200fe
Add new tests
Mar 18, 2017
33eb740
Address requested changes
Mar 18, 2017
654288b
Fix Travis errors
Mar 18, 2017
5bf1508
Address requested changes
Mar 20, 2017
9e39794
Address requested changes
Mar 20, 2017
968c7f1
DOC/TST: change to use parameterization
jreback Mar 25, 2017
8d2e9cc
Address requested changes
Mar 28, 2017
73df69e
Address requested changes
Mar 28, 2017
64e86a4
Fix test on right join
Mar 28, 2017
2d4e143
Fix pytest fixture name collision
Mar 28, 2017
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11 changes: 2 additions & 9 deletions doc/source/whatsnew/v0.20.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -740,8 +740,8 @@ New Behavior:

.. _whatsnew_0200.api_breaking.index_order:

Index order after inner join due to Index intersection
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Index.intersection and inner join now preserve the order of the left Index
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The ``Index.intersection`` now preserves the order of the calling Index (left)
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say what this did previously. No need to mention Index.join or DataFrame.merge and say .align methods. simpler is better.

instead of the other Index (right) (:issue:`15582`). This affects the inner
Expand Down Expand Up @@ -788,18 +788,11 @@ joins (methods ``DataFrame.join`` and ``pd.merge``) and the .align methods.
1 10 100
2 20 200

In [5]: pd.merge(df1, df2, how='inner', left_index=True, right_index=True)
Out[5]:
a b
1 10 100
2 20 200

New Behavior:

.. ipython:: python

df1.join(df2, how='inner')
pd.merge(df1, df2, how='inner', left_index=True, right_index=True)


.. _whatsnew_0200.api:
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9 changes: 6 additions & 3 deletions pandas/core/frame.py
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Expand Up @@ -124,9 +124,12 @@
----------%s
right : DataFrame
how : {'left', 'right', 'outer', 'inner'}, default 'inner'
* left: use only keys from left frame (SQL: left outer join)
* right: use only keys from right frame (SQL: right outer join)
* outer: use union of keys from both frames (SQL: full outer join)
* left: use only keys from left frame (SQL: left outer join), preserving
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nit: can you format these lines like

* right: use only keys from right frame
     similar to a SQL: right outer join; preserves key orderings

their order
* right: use only keys from right frame (SQL: right outer join), preserving
their order
* outer: use union of keys from both frames (SQL: full outer join), and
sort them lexicographically
* inner: use intersection of keys from both frames (SQL: inner join),
preserving the order of the left keys
on : label or list
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2 changes: 2 additions & 0 deletions pandas/indexes/base.py
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Expand Up @@ -2844,6 +2844,8 @@ def _reindex_non_unique(self, target):
level : int or level name, default None
return_indexers : boolean, default False
sort : boolean, default False
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add a versionadded tag

Sort the join keys lexicographically in the result Index. If False,
the order of the join keys depends on the join type (how keyword)

.. versionadded:: 0.20.0
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can you add a sentence explaining what sort does (I know its repeatative, but this is a different part of the code)


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6 changes: 3 additions & 3 deletions pandas/tests/frame/test_join.py
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Expand Up @@ -20,7 +20,7 @@ def df1():

@pytest.fixture
def df2():
return DataFrame({'b': [100, 200, 300]}, index=[1, 2, 3])
return DataFrame({'b': [300, 100, 200]}, index=[3, 1, 2])


@pytest.mark.parametrize(
Expand All @@ -37,8 +37,8 @@ def df2():
('left', True, DataFrame({'a': [0, 10, 20],
'b': [np.nan, 100, 200]},
index=[0, 1, 2])),
('right', False, DataFrame({'a': [10, 20, np.nan],
'b': [100, 200, 300]},
('right', False, DataFrame({'a': [np.nan, 10, 20],
'b': [300, 100, 200]},
index=[1, 2, 3])),
('right', True, DataFrame({'a': [10, 20, np.nan],
'b': [100, 200, 300]},
Expand Down