BUG: groupby.apply drops the group key

[pyarchana]

No description provided.

[precedent-bot]

From pandas-dev/pandas review history

Nobody asked me. I read the files this pull request changes and found three conventions the project has settled before, each linked to where it was settled.

• Always include a whatsnew entry in the appropriate file for any bug fixes or new features.
  Established in pandas-dev/pandas#64119 and #61985.

  Raised because it changes doc/source/whatsnew/v3.0.0.rst.

  This helps keep the documentation up to date and informs users of changes.

• Use the code-block directive for demonstrating old behavior and the ipython directive for newly introduced behavior in the whatsnew files.
  Established in pandas-dev/pandas#63310 and #50626.

  Raised because it changes doc/source/whatsnew/v3.0.0.rst.

  This approach helps maintain clarity and accuracy in documenting changes across different versions of pandas.

• The first line of a docstring should be a single line summary.
  Established in pandas-dev/pandas#62880 and #36371.

  Raised because it changes pandas/core/frame.py.

  This helps maintain consistency and clarity in documentation across the project.

If this is wrong or out of date, a maintainer can say so: reply @precedent <the convention as it actually is> and I will hold the correction from then on.

[pyarchana]

@precedent every public function needs a docstring with a one line summary

[precedent-bot]

Recorded, from pyarchana.

Every public function must have a docstring that includes a one line summary.

I already held this. Your statement is added as further evidence rather than as a duplicate rule.

Answers from here on cite this, attributed to you rather than inferred from a pattern. If the wording is wrong, say it again and I will hold the newer one.