[jira] [Commented] (ARROW-10640) [C++] A "where" kernel to combine two arrays based on a mask

["Antoine Pitrou (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-10640?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17234451#comment-17234451 ] 

Antoine Pitrou commented on ARROW-10640:
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A boolean entry can be true, false or null. Shouldn't the kernel combine three arrays? (of course, you're free to pass the same input twice).

> [C++] A "where" kernel to combine two arrays based on a mask
> ------------------------------------------------------------
>
>                 Key: ARROW-10640
>                 URL: https://issues.apache.org/jira/browse/ARROW-10640
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: C++
>            Reporter: Joris Van den Bossche
>            Priority: Major
>
> (from discussion in ARROW-9489 with [~maartenbreddels])
> A general "where" kernel like {{np.where}} (https://numpy.org/doc/stable/reference/generated/numpy.where.html) seems a generally useful kernel to have, and could also help mimicking some other python (setitem-like) operations. 
> The concrete use case in ARROW-9489 is to basically do a {{fill_null(array[string], array[string])}} which could be expressed as {{where(is_null(arr), arr2, arr)}}. 



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