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BUG: right merge not preserve row order (#27453) #27762

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BUG: right merge not preserve row order (#27453) #27762

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c3565c7
add failing test to check row order preservation
Aug 2, 2019
0e481a7
correct the imports
Aug 2, 2019
42eaad1
change order of args in test assertion
Aug 2, 2019
3bba941
broken commit with a bunch of print statements and comments
Aug 2, 2019
803243c
add test for left merge
Aug 5, 2019
cc269f3
swap left and right keys when how == "right"
Aug 5, 2019
f2249df
correct old test: right-merge row order is now the same as the right df
Aug 5, 2019
5f728a4
clean up spacing and delete temp code
Aug 5, 2019
7ccebb2
add whatsnew
Aug 10, 2019
90984e4
replace .from_records with default constructor
Aug 12, 2019
de44eae
add GH issue # to tests
Aug 12, 2019
a8954fe
revert commit ed54bec7e
Aug 13, 2019
d328470
change logic to swap left and right if how==right
Aug 13, 2019
3c1a7cb
clean formatting
Aug 13, 2019
7fc6441
rename vars and add comment for clarity
Sep 21, 2019
1e9df2b
combine tests into one
Sep 21, 2019
d017bd5
update whatsnew
Sep 21, 2019
71736b8
Update doc/source/whatsnew/v1.0.0.rst
Sep 28, 2019
11ec7d0
add before and after examples
Oct 26, 2019
c238b50
linting
Nov 2, 2019
e29ed1c
cleanup
Jan 1, 2020
2b1b675
changes requested by jreback
Jan 23, 2020
ef14ba0
update docs
Jan 23, 2020
978f91f
Merge branch 'master' into 27453-right-merge-order
Jan 23, 2020
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rename vars and add comment for clarity
  • Loading branch information
Nico Cernek committed Jan 1, 2020
commit 7fc644174583c67d09bd52d100732240a124c028
8 changes: 5 additions & 3 deletions pandas/core/reshape/merge.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1319,17 +1319,19 @@ def _get_join_indexers(
# `count` is the num. of unique keys
# set(lkey) | set(rkey) == range(count)

# flip left and right keys if performing a right merge
# to preserve right merge row order (GH 27453)
if how == "right":
rkey, lkey, count = fkeys(rkey, lkey)
factorized_rkey, factorized_lkey, count = fkeys(rkey, lkey)
else:
lkey, rkey, count = fkeys(lkey, rkey)
factorized_lkey, factorized_rkey, count = fkeys(lkey, rkey)
# preserve left frame order if how == 'left' and sort == False
kwargs = copy.copy(kwargs)
if how == "left":
kwargs["sort"] = sort
join_func = _join_functions[how]

return join_func(lkey, rkey, count, **kwargs)
return join_func(factorized_lkey, factorized_rkey, count, **kwargs)


def _restore_dropped_levels_multijoin(
Expand Down