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

["Ian Cook (Jira)" <ji...@apache.org>]

Ian Cook created ARROW-13064:
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             Summary: [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


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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