Add join_asof/3

[0x009922]

I have added some changes on top of #1080:

• Refined docs (mostly copied from Polars Python API);
• Validating :on to be a single column (join_asof currently works only with a single column)
• Chore refactors (restore Cargo.toml; reduce boilerplate of :on/:by normalisation).

Maybe as part of this PR, or as a separate one, would be nice to add other options supported by Polars:

• :tolerance
• :allow_eq
• :check_sortedness

[billylanchantin]

Thanks, this looks great! It's also been in my queue for quite a while, so I appreciate you getting it across the finish line.

Maybe as part of this PR, or as a separate one, would be nice to add other options supported by Polars:

I leave that up to you. I'd be happy to merge this essentially as is, then you can add the additional options as a follow-on if you like.

My only quibble is that I find the explanation of by a bit lacking. (The Polars docs are the real culprit here.) I had to do a few tests in console of that option before I understood the intended behavior.

[0x009922]

Thank you for the review!

I leave that up to you. I'd be happy to merge this essentially as is, then you can add the additional options as a follow-on if you like.

I think adding them as a follow-on is easier for everyone.

My only quibble is that I find the explanation of by a bit lacking. (The Polars docs are the real culprit here.) I had to do a few tests in console of that option before I understood the intended behavior.

I would agree... Perhaps, I could add a few more tests showing in more depth how by works (and figure it out myself).

[billylanchantin]

I went a little overboard and attempted a rewrite of the Examples section.

After rereading, I found the examples that Polars chose a little confusing. I think my brain just doesn't parse the dates fast enough to follow super easily.

My intended audience is someone who knows what a left join is but hasn't encountered the "asof" join before. LMK if you think this is better. I'm also happy to go with something else!

[0x009922]

It seems there is nothing left to add to this PR. Or would you like me to change something else?

[billylanchantin]

No this is awesome, thanks again! ❤️

[jeregrine]

❤️💜

[billylanchantin]

Yeah thanks to @jeregrine as well for getting this started! The "asof" join has been useful to me on a number of occasions and I'm really glad we can incorporate it :)