BUG: groupby.apply incorrectly dropping nan

[debnathshoham]

• closes Combination of groupby with dropna set to True and apply function not returning expected output #43205
• tests added / passed
• Ensure all linting tests pass, see here for how to run them
• whatsnew entry

[debnathshoham]

since this is a regression, shouldn't this go to 1.3.3?

[jreback]

this looks fine
cc @rhshadrach

[rhshadrach]

Thanks for the PR - looks great.

[rhshadrach]

This test completely supersedes the other test_apply_dropna_with_indexed test; can you just apply the parametrization and the expected change to that test.

[debnathshoham]

Amended.
Let me know how this looks.

[rhshadrach]

lgtm

[jreback]

thanks @debnathshoham

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout 1.3.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 99640224fbe3ec14b8775492471d5d915093bfba

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #43236: BUG: groupby.apply incorrectly dropping nan'

4. Push to a named branch :

git push YOURFORK 1.3.x:auto-backport-of-pr-43236-on-1.3.x

5. Create a PR against branch 1.3.x, I would have named this PR:

"Backport PR #43236 on branch 1.3.x (BUG: groupby.apply incorrectly dropping nan)"

And apply the correct labels and milestones.

Congratulation you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove Still Needs Manual Backport label once the PR gets merged.

If these instruction are inaccurate, feel free to suggest an improvement.

[jreback]

@meeseeksdev backport 1.3.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout 1.3.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 99640224fbe3ec14b8775492471d5d915093bfba

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #43236: BUG: groupby.apply incorrectly dropping nan'

4. Push to a named branch :

git push YOURFORK 1.3.x:auto-backport-of-pr-43236-on-1.3.x

5. Create a PR against branch 1.3.x, I would have named this PR:

"Backport PR #43236 on branch 1.3.x (BUG: groupby.apply incorrectly dropping nan)"

And apply the correct labels and milestones.

Congratulation you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove Still Needs Manual Backport label once the PR gets merged.

If these instruction are inaccurate, feel free to suggest an improvement.

[jreback]

@debnathshoham if you can follow the instructions above and manually backport