Implementation of group_by+mutate

[dafxy]

The implementation makes it consistent with the tidyverse sintax.

[dafxy]

This solves issue #201. Other functions to be applied to grouped data can be easily implemented in the same fashion.

[dafxy]

Needs a little tweek here:
self.by = by if isinstance(by, list) else [by]

[markfairbanks]

Apologies for the long response time on this - I will take a look either this weekend or early next week. I think with the polars v1.0.0 release (now on v1.6.0) it's time to resurrect tidypolars and get it back to working form.

[markfairbanks]

Can you break this into multiple pull requests?

[markfairbanks]

I'm starting to review but there are multiple parts - it would be nice to address each addition separately. For each part we need to discuss code changes and tests (none of these functions have tests as of yet).

Can you pick one of these to start with at least? If you do group_by() feel free to include both mutate() and filter()
These are the additions:

• group_by()
  • mutate()
  • filter()
• nest()/unnest()
• crossing()
• distinct(keep_all = )
• as_factor()
• replace() (I don't think this belongs in tidypolars but we can discuss)

[dafxy]

Feel free to cherry-pick each commit in the repo.

[markfairbanks]

We can try and do it all in one but this is an overly large PR at the moment. Moving forward each PR must have a (generally) unique purpose.

Some of these pieces could be merged tomorrow with very little effort whereas others are going to take a while to update - which means none of this is getting merged for a while (I could be wrong maybe it will go faster than I think).

[markfairbanks]

Here's my first pass at a review.

All functions also need tests and to be added to the changelog

[dafxy]

How do you think we should go about the changes above? They are pretty straightforward.

[markfairbanks]

Just make the commits on your repo. Once all the changes are done with tests and changelog we're good to merge.

[markfairbanks]

If you need ideas for tests my tidytable repository is good place to grab them
https://github.com/markfairbanks/tidytable/tree/main/tests/testthat

[markfairbanks]

If you haven't used pytest let me know and I can walk you through it

[dafxy]

All done, except for the test. If you or someone could implement the tests, that would be great.

[markfairbanks]

I can help a little with tests, but you’ll need to build some here (and in every pull request). In general for every PR you need the function, a test or a two, and to update the changelog.