add the 'name' attribute to dataframes that go through apply_frame_axis0

[llllllllll]

• closes #xxxx
• tests added / passed
• passes git diff upstream/master | flake8 --diff
• whatsnew entry

Previously, if you did group.name in the applied function, it would fail and fall back to the slower path because the attribute did not exist.

shape_before was unused.

[codecov-io]

Current coverage is 85.97% (diff: 100%)

Merging #15062 into master will decrease coverage by <.01%

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[jreback]

looks innocuous enough (famous last words).

did you have a higher level usage that was triggering this?

[jreback]

can you add an asv for this?

and add a whatsnew note (perf improvements).

[jreback]

ping @llllllllll

[llllllllll]

Sorry about letting this sit idle. I will try to get the asv report and what's new on Monday.

[jreback]

np, ping when ready.

[llllllllll]

ping: I ran the suite locally but it was pretty noisy. I won't be run this without having other stuff running in the background until sometime tonight.

[jreback]

@llllllllll lgtm.

just report on perf when you can.

I also think that the .name arg is somewhat undocumented when passed to .apply, if you want to add a note there (or small example), might be useful.

[jreback]

@llllllllll can you rebase; ping on green. i think this was ok.

[llllllllll]

from what I remember I was going to add a performance case for the asv suite. I had one locally but I actually saw a performance regression and didn't have time to dig deeper. I can rebase but I am not sure if we want to merge with the open question.

[jreback]

@llllllllll looks like you add an example in the asv. if you can rebase and just show/before after on that example would be fine.

[jreback]

thanks @llllllllll rebased and merged.