[jira] [Commented] (ARROW-15455) [C++] Cast between fixed size list type and variable size list

["Eduardo Ponce (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-15455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17500378#comment-17500378 ] 

Eduardo Ponce commented on ARROW-15455:
---------------------------------------

Also need to consider the scalar cases:
{code:python}
>>> fixed_size = pa.scalar([1, 2], type=pa.list_(pa.int64(), 2))
>>> fixed_size.cast(pa.list_(pa.int64()))
pyarrow.lib.ArrowNotImplementedError: casting scalars of type fixed_size_list<item: int64>[2] to type list<item: int64>
{code}

> [C++] Cast between fixed size list type and variable size list 
> ---------------------------------------------------------------
>
>                 Key: ARROW-15455
>                 URL: https://issues.apache.org/jira/browse/ARROW-15455
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Joris Van den Bossche
>            Assignee: Jabari Booker
>            Priority: Major
>              Labels: good-second-issue, kernel, pull-request-available
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> Casting from fixed size list to variable size list could be possible, I think, but currently doesn't work:
> {code:python}
> >>> fixed_size = pa.array([[1, 2], [3, 4]], type=pa.list_(pa.int64(), 2))
> >>> fixed_size.cast(pa.list_(pa.int64()))
> ...
> ArrowNotImplementedError: Unsupported cast from fixed_size_list<item: int64>[2] to list using function cast_list
> {code}
> And in principle, a cast the other way around could also be possible if it is checked that each list has the correct length.



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