[ENH] Introducing test file for polars support for estimators

[julian-fong]

Reference Issues/PRs

#342 is the linked issue that overlays the entire workflow for polars support. Opening this thread mainly for the test file I am planning to implement for polars support in skpro

What does this implement/fix? Explain your changes.

Implements a test file for testing various fit/predict functions using polars dataframes. Ideas for any tests regarding testing polars support in skpro is much appreciated!

Does your contribution introduce a new dependency? If yes, which one?

No, it does not introduce a new dependency

What should a reviewer concentrate their feedback on?

I was going through a couple regression estimators glm , and quickly realized that the underlying dependency statsmodels currently do not support polars dataframes as inputs for their fit functions. Since that is the case, it seems like conversion between polars to pandas must be necessary in order to allow fitting (and I would assume predicting) to happen.

@fkiraly Would this be the correct approach to deal with estimators that do not potentially have underlying polars support in them?

[julian-fong]

a follow up question: what is the expectation if currently some of the estimators are coded to return pandas dataframes. As an example, in regression.mapie, the _predict function turns y_pred into a pandas Dataframe and returns that as an output.

Should we approach writing this test file under the assumption that all estimators have the capability/functionality to return polars Dataframes?

[fkiraly]

what is the expectation if currently some of the estimators are coded to return pandas dataframes. As an example, in regression.mapie, the _predict function turns y_pred into a pandas Dataframe and returns that as an output.

afaik, the boilerplate layer, i.e., BaseProbaRegerssor.predict, will turn it back into a polars.DataFrame if that was passed initially to fit. In the tests, I would check that this is indeed the case.

[fkiraly]

let me know if/when you would like a review (even if not finished)

[julian-fong]

Some of the CLI failures look weird - they are just long empty pages.

[julian-fong]

If i am trying to test an estimator say in test_polars_eager_regressor_in_fit_predict, what is the best approach to do so?