[jira] [Commented] (ARROW-5005) [C++] Implement support for using selection vectors in scalar aggregate function kernels

["Niranda Perera (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-5005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17359389#comment-17359389 ] 

Niranda Perera commented on ARROW-5005:
---------------------------------------

I will take this up. From what I understand, we need to enable masked scalar aggregates using the `ExecBatch::selection_vector`.

I have a couple of questions.
 # Where/ at what point would the selection_vector be set to an ExecBatch?
 # Should I change the kernels in aggregate_* files, so that they are selection-vector-aware, or should we manage those as separate implementations?

> [C++] Implement support for using selection vectors in scalar aggregate function kernels
> ----------------------------------------------------------------------------------------
>
>                 Key: ARROW-5005
>                 URL: https://issues.apache.org/jira/browse/ARROW-5005
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Francois Saint-Jacques
>            Assignee: Niranda Perera
>            Priority: Major
>
> The aggregate kernels don't support mask (the result of a filter). Add the the following method to `AggregateFunction`.
> {code:c++}
> virtual Status ConsumeWithFilter(const Array& input, const Array& mask, void* state) const = 0;
> {code}
> The goal is to add support for AST similar to:
> {code:sql}
> SELECT AGG(x) FROM table WHERE pred;
> {code}



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