BUG: GH12824 fixed apply() returns different result depending on whet…

[adneu]

• closes groupby().apply() returns different result depends on the first result is None or not. #12824
• tests added / passed
• passes git diff upstream/master | flake8 --diff
• whatsnew entry

In _wrap_applied_output for NDFrameGroupBy, if the first result of apply is None, find the first non-None result to determine behavior

[jreback]

make this a helper function in core/groupby.py (and consolidate the other one which has the same code)

[jreback]

can you rebase / update

[adneu]

Rebased and made the changes you suggested but there was a new error with the test. It is introduced by #12743 which now throws an error in _concat_objects when any of the values are None (see below). The new PR makes a small change to deal with this, can you check if ok?

======================================================================
ERROR: test_groupby_apply_none_first (pandas.tests.test_groupby.TestGroupBy)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ".../pandas/tests/test_groupby.py", line 6292, in test_groupby_apply_none_first
    result = test_df.groupby('groups').apply(test_func)
  File ".../pandas/core/groupby.py", line 651, in apply
    return self._python_apply_general(f)
  File ".../pandas/core/groupby.py", line 660, in _python_apply_general
    not_indexed_same=mutated or self.mutated)
  File ".../pandas/core/groupby.py", line 3241, in _wrap_applied_output
    not_indexed_same=not_indexed_same)
  File ".../pandas/core/groupby.py", line 824, in _concat_objects
    values = reset_identity(values)
  File ".../pandas/core/groupby.py", line 809, in reset_identity
    ax = v._get_axis(self.axis)
AttributeError: 'NoneType' object has no attribute '_get_axis'

----------------------------------------------------------------------

[jreback]

I think we can remove the _count_not_none(....)

[codecov-io]

Current coverage is 84.12%

Merging #12977 into master will increase coverage by <.01%

@@             master     #12977   diff @@
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  Files           138        138          
  Lines         50388      50390     +2   
  Methods           0          0          
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+ Hits          42386      42388     +2   
  Misses         8002       8002          
  Partials          0          0          

1. 4 files (not in diff) in pandas were modified. more
   • Hits -4

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[jreback]

can you squash

[jreback]

thanks @adneu