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

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

Weston Pace created ARROW-16549:
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             Summary: [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


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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