separate `pl.list()` and `pl.concat_list`

[mcrumiller]

separate `pl.list()` and `pl.concat_list`

[NickCrews]

This is the exact semantics I want!

Except may I recommend the signature of list() be
Def list(vals: Iterable, *, dtype=None) this would match the API of pythons list(), it would allow for idempotency, and the dtype allows you to pass in a 0 length array and still know the type.

We are solving this exact same thing in ibis-project/ibis#9473

[stinodego]

This was discussed in the linked issue. I don't believe adding a separate list function adds much, besides some additional input validation. I'll close this as not planned for now.

[mcrumiller]

@stinodego how would one collect a list of pl.List(...) columns into an outer list? As in take:

df = pl.DataFrame({
    "a": [[1, 2, 3]],
    "b": [[4, 5, 6]],
})

concatenating the columns into a list:

shape: (1, 1)
┌────────────────────────┐
│ literal                │
│ ---                    │
│ list[list[i64]]        │
╞════════════════════════╡
│ [[1, 2, 3], [4, 5, 6]] │
└────────────────────────┘

AFAIK there's no way to do this, because concat_list is designed to flatten lists, and there is no general method for converting columns into list elements.

[NickCrews]

See my comment in the linked issue, it describes exactly what @mcrumiller talks about, we would need to add special-casing code to ibis in order to be able to support this.