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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