Multiply all element of an array by value of another column

[tim-x-y-z]

Problem description

It would fantastic if i could just do:

>>> df=pl.DataFrame({"a": [[1,2,3], [3,4,5]], "b": [0.5, 0.1]})
>>> df.with_columns(
...     new_col=pl.col("a").list.eval(pl.element() * pl.col("b") * 2)
... )

but this currently yields:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/tim/Documents/Github/ercot-wind-optimisation/.venv/lib/python3.11/site-packages/polars/dataframe/frame.py", line 7335, in with_columns
    .collect(no_optimization=True)
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tim/Documents/Github/ercot-wind-optimisation/.venv/lib/python3.11/site-packages/polars/lazyframe/frame.py", line 1531, in collect
    return wrap_df(ldf.collect())
                   ^^^^^^^^^^^^^
exceptions.ComputeError: named columns are not allowed in `list.eval`; consider using `element` or `col("")`

on version 0.18.7

On a side note, the error is counter intuitive as here i am using pl.col("").

[ritchie46]

Duplicate of #9188 and #8006

[ritchie46]

For the record, it is planned, but let's keep discussion in the existing issues.

[stinodego]

Yeah, the GitHub UI is confusing here. It says "closed as not planned" but the description is "Won't fix, can't repro, duplicate, stale". In this case it's a duplicate.