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https://issues.apache.org/jira/browse/ARROW-13064?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17364358#comment-17364358
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David Li commented on ARROW-13064:
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There's also one complication in that it looks like variadic functions don't
currently allow mixed types. So we'll have to extend the kernel infra to allow
this, or pack arguments in struct types.
> [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
> 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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