fix(rust, python): handle concat_list with first lit value

[josh]

The first value passed to pl.concat_list receives some special treatment being the lhs. This means that using a pl.lit or any unit series doesn't get expanded as expected. Using a unit value in any other position works as you'd expected.

Example:

pl.DataFrame({"a": [1, 2, 3]}).select(
  pl.concat_list([pl.lit(1), pl.col("a")])
)
# ShapeError: length 3 does not match 1

Related #7236
Tangentially related #6608

[josh]

Is there a nicer Rust pattern for handling this reassignment? The compiler really wanted this new series to have a scope outside the if statement to let me reassign it.

[ritchie46]

That's because new_ca would get dropped when the scope ends.

You can clone on line 144. Then you can assign directly

[josh]

Ah! Thanks for that explanation. Still new to Rust. Does to_owned() offer any benefit over clone() there? I'm not sure how expensive a clone() on a ChunkedArray. Does it end up doing a deep copy of all it's items or just the wrapping type?

[ritchie46]

Does it end up doing a deep copy of all it's items or just the wrapping type?

The data is wrapped by an Arc so it is a cheap clone.

[ritchie46]

Thanks!

[ritchie46]

That's because new_ca would get dropped when the scope ends.

You can clone on line 144. Then you can assign directly