Implement $sample() for DataFrame

[etiennebacher]

No description provided.

[sorhawell]

Thanks @etiennebacher !

This PR as is I think was fine. However I have some minor details.

In the past rust-polars errors where often just converted into a String, but we try to avoid that in any new or refactored code. For complicated trait-rule-reasons we cannot currently just use the ?-operator to convert rust-polars PolarsError to our r-polars RPolarsError (but likely in future version of rust we can). We have to use the polars_to_rpolars_err() function for now, but it will ensure our canonical conversion is used.

avoid stop() outside a result() as it will raise an unstyled error with no context, which can be difficult for user to interpret if coming from somewhere unknown in a large polars syntax query.

result catches any error and upgrades it, so inside a result clause stop() is fine. Otherwise for Err_plain() is effectively the same outcome with fewer internal steps.

> result(stop("oups")) |> unwrap("in some example_function():")
Error: Execution halted with the following contexts
   0: In R: in some example_function():
   0: During function call [unwrap(result(stop("oups")), "in some example_function():")]
   1: oups
   
> Err_plain("oups") |> unwrap("example_function():")
Error: Execution halted with the following contexts
   0: In R: example_function():
   0: During function call [unwrap(Err_plain("oups"), "example_function():")]
   1: oups

all the pcase stuff is not mandatory

[eitsupi]

Thanks!

[etiennebacher]

Thanks for finishing this PR @sorhawell

In the past rust-polars errors where often just converted into a String, but we try to avoid that in any new or refactored code. For complicated trait-rule-reasons we cannot currently just use the ?-operator to convert rust-polars PolarsError to our r-polars RPolarsError (but likely in future version of rust we can). We have to use the polars_to_rpolars_err() function for now, but it will ensure our canonical conversion is used.

Yes I feel like you explained this to me before but I didn't remember. We should probably refactor functions on the Rust side to use this (I can try to do this for a couple of them and then ask you to check)