[jira] [Assigned] (ARROW-13064) [C++] Add a general "if, ifelse, ..., else" kernel

["David Li (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-13064?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

David Li reassigned ARROW-13064:
--------------------------------

    Assignee: David Li

> [C++] Add a general "if, ifelse, ..., else" kernel
> --------------------------------------------------
>
>                 Key: ARROW-13064
>                 URL: https://issues.apache.org/jira/browse/ARROW-13064
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Ian Cook
>            Assignee: David Li
>            Priority: Major
>
> ARROW-10640 added a ternary {{if_else}} kernel. Add another kernel that extends this concept to an arbitrary number of conditions and associated results, like a vectorized {{if-ifelse-...-else}} with an arbitrary number of {{ifelse}} and with the {{else}} optional. This is like a SQL {{CASE}} statement.
> How best to achieve this is not obvious. To enable SQL-style uses, it would be most efficient to implement this as a variadic kernel where the even-number arguments (0, 2, ...) are the arrays of boolean conditions, the odd-number arguments (1, 3, ...) are the corresponding arrays of results, and the final argument is the {{else}} result. But I'm not sure if this is practical. Maybe instead we should implement this to operate on listarrays, like NumPy's {{[np.where|https://numpy.org/doc/stable/reference/generated/numpy.where.html]}} or {{[np.select|https://numpy.org/doc/stable/reference/generated/numpy.select.html]}}.



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