BUG: grouby(axis=1) cannot select column names

[charlesdong1991]

• closes GroupBy(axis=1) Does Not Offer Implicit Selection By Columns Name(s) #27614
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[pep8speaks]

Hello @charlesdong1991! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-08-02 07:54:46 UTC

[TomAugspurger]

Should be DataFrame.groupby`

"does not offer" to "not offering"

"axis set to 1" to "axis=1"

[TomAugspurger]

I'm also not sure what "implicit selection by column name" means here.

[charlesdong1991]

I'm also not sure what "implicit selection by column name" means here.

ahh, my bad, i basically just copied and pasted the issue title, will change! @TomAugspurger thanks for your quick reply!

[WillAyd]

Nice looking PR! Can you add a test case for a multi index column as well?

[codecov]

Codecov Report

Merging #27700 into master will decrease coverage by 50.51%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##           master   #27700       +/-   ##
===========================================
- Coverage      93%   42.49%   -50.52%     
===========================================
  Files         182      182               
  Lines       50195    50195               
===========================================
- Hits        46686    21328    -25358     
- Misses       3509    28867    +25358

Flag	Coverage Δ
#multiple	?
#single	42.49% <0%> (-0.09%)	⬇️

Impacted Files	Coverage Δ
pandas/core/groupby/grouper.py	18.38% <0%> (-80.15%)	⬇️
pandas/io/formats/latex.py	0% <0%> (-100%)	⬇️
pandas/io/gcs.py	0% <0%> (-100%)	⬇️
pandas/io/sas/sas_constants.py	0% <0%> (-100%)	⬇️
pandas/tseries/plotting.py	0% <0%> (-100%)	⬇️
pandas/tseries/converter.py	0% <0%> (-100%)	⬇️
pandas/io/s3.py	0% <0%> (-100%)	⬇️
pandas/io/formats/html.py	0% <0%> (-99.38%)	⬇️
pandas/io/sas/sas7bdat.py	0% <0%> (-91.16%)	⬇️
pandas/io/sas/sas_xport.py	0% <0%> (-90.1%)	⬇️
... and 137 more

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[charlesdong1991]

@WillAyd @TomAugspurger I added tests for MI columns, and seems work well and pass all tests! Feel free to take a look again!

[jreback]

thanks @charlesdong1991

[jreback]

these might be closable now: #21127, #17961, #13420, #3689

[charlesdong1991]

thanks for merge!
I will double check those cases @jreback shall I create another PR to add test for those cases? If tests not passed, then I will create other PRs to debug and fix those issues