Refactor groupby behavior, add agg function to Checks, support error callback option

[cosmicBboy]

Is your feature request related to a problem? Please describe.

This issue tackles several problems with the related theme of producing more informative error messages in Checks, see discussion in #429.

Describe the solution you'd like

The outcome of the discussion is described in https://github.com/pandera-dev/pandera/issues/429#issuecomment-811045571

• [ ] refactor groupby behavior to expect a pandas Groupby object (breaking change)
• [ ] add agg kwarg to Check that simply wraps DataFrame.agg and Series.agg depending on the schema context
• [ ] support callback function for the error kwarg:

CheckObj = Union[pd.Series, pd.DataFrame, pd.Groupby]  # series or dataframe can be the output of `agg` operation

def error_callback(check_obj: CheckObj, check_output) -> str:
    return f"check failed with values {check_obj}, check output: {check_output}"

[cmhac]

What's the status of this? I'm running into a use case where I need the exact functionality described in #872.

I'm currently just raising an error in the check if it fails to help debug, but would love to have this be part of the tool.

[cosmicBboy]

hi @christopher-hacker this is ready to be worked on, no one is currently owning this. Would you be interested in making a contribution?