[jira] [Updated] (ARROW-17463) [R] Avoid unnecessary projections

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-17463?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

ASF GitHub Bot updated ARROW-17463:
-----------------------------------
    Labels: pull-request-available  (was: )

> [R] Avoid unnecessary projections
> ---------------------------------
>
>                 Key: ARROW-17463
>                 URL: https://issues.apache.org/jira/browse/ARROW-17463
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: R
>            Reporter: Neal Richardson
>            Assignee: Neal Richardson
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 10.0.0
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> In ExecPlan$Build(), we call Project in a few places, and there is code to make sure that there is at least one ProjectNode in the query in order to remove augmented fields from a Dataset scan (unless the user has added them). As a result, it is possible to get multiple ProjectNodes in a row that are essentially no-op. One example is with grouped aggregation: there is a projection to get the order of the columns back to what R expects, and then a no-op projection after that:
> {code}
> > mtcars |> arrow_table() |> count(cyl) |> explain()
> ExecPlan with 6 nodes:
> 5:SinkNode{}
>   4:ProjectNode{projection=[cyl, n]}
>     3:ProjectNode{projection=[cyl, n]}
>       2:GroupByNode{keys=["cyl"], aggregates=[
>       	hash_sum(n, {skip_nulls=true, min_count=1}),
>       ]}
>         1:ProjectNode{projection=["n": 1, cyl]}
>           0:TableSourceNode{}
> {code}
> IDK how significant of a performance impact this would have, but it certainly looks wasteful and should be avoidable.



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