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https://issues.apache.org/jira/browse/ARROW-18185?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17628751#comment-17628751
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Joris Van den Bossche commented on ARROW-18185:
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> What about implementing this as an specialized optimization for if_else AAS
> case,
That sounds good to me
> [C++][Compute] Support KEEP_NULL option for compute::Filter
> -----------------------------------------------------------
>
> Key: ARROW-18185
> URL: https://issues.apache.org/jira/browse/ARROW-18185
> Project: Apache Arrow
> Issue Type: New Feature
> Components: C++
> Reporter: Jin Shang
> Assignee: Jin Shang
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 50m
> Remaining Estimate: 0h
>
> The current Filter implementation always drops the filtered values. In some
> use cases, it's desirable for the output array to have the same size as the
> inut array. So I added a new option FilterOptions::KEEP_NULL where the
> filtered values are kept as nulls.
> For example, with input [1, 2, 3] and filter [true, false, true], the current
> implementation will output [1, 3] and with the new option it will output [1,
> null, 3]
> This option is simpler to implement since we only need to construct a new
> validity bitmap and reuse the input buffers and child arrays. Except for
> dense union arrays which don't have validity bitmaps.
> It is also faster to filter with FilterOptions::KEEP_NULL according to the
> benchmark result in most cases. So users can choose this option for better
> performance when dropping filtered values is not required.
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