[jira] [Resolved] (ARROW-16549) [C++] Simplify AggregateNodeOptions aggregates/targets

["Weston Pace (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-16549?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Weston Pace resolved ARROW-16549.
---------------------------------
    Fix Version/s: 9.0.0
       Resolution: Fixed

Issue resolved by pull request 13150
[https://github.com/apache/arrow/pull/13150]

> [C++] Simplify AggregateNodeOptions aggregates/targets
> ------------------------------------------------------
>
>                 Key: ARROW-16549
>                 URL: https://issues.apache.org/jira/browse/ARROW-16549
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Weston Pace
>            Assignee: Vibhatha Lakmal Abeykoon
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 9.0.0
>
>          Time Spent: 7h 10m
>  Remaining Estimate: 0h
>
> Currently AggregateNodeOptions is:
> {noformat}
> class ARROW_EXPORT AggregateNodeOptions : public ExecNodeOptions {
>  public:
>   // aggregations which will be applied to the targetted fields
>   std::vector<internal::Aggregate> aggregates;
>   // fields to which aggregations will be applied
>   std::vector<FieldRef> targets;
>   // output field names for aggregations
>   std::vector<std::string> names;
>   // keys by which aggregations will be grouped
>   std::vector<FieldRef> keys;
> };
> {noformat}
> It is not very obvious how {{aggregates}} and {{targets}} are related.  My initial read of the comments led me to think that each aggregate would be applied to each target and you would end up with {{len(aggregates) * len(targets)}} output fields.  In reality the {{aggregate}} at index {{i}} only applies to the {{target}} at index {{i}}.  It would be simpler to add a {{FieldRef target}} to {{internal::Aggregate}} (and {{Aggregate}} should not be {{internal}}).
> Alternatively, the entire {{internal::Aggregate}} could be replaced by a "call" {{arrow::compute::Expression}}



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