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https://issues.apache.org/jira/browse/ARROW-12632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17617227#comment-17617227
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Apache Arrow JIRA Bot commented on ARROW-12632:
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This issue was last updated over 90 days ago, which may be an indication it is
no longer being actively worked. To better reflect the current state, the issue
is being unassigned per [project
policy|https://arrow.apache.org/docs/dev/developers/bug_reports.html#issue-assignment].
Please feel free to re-take assignment of the issue if it is being actively
worked, or if you plan to start that work soon.
> [C++][Dataset][Compute] Add support for dictionary_encode to Expression
> -----------------------------------------------------------------------
>
> Key: ARROW-12632
> URL: https://issues.apache.org/jira/browse/ARROW-12632
> Project: Apache Arrow
> Issue Type: New Feature
> Components: C++
> Affects Versions: 4.0.0
> Reporter: Ben Kietzman
> Assignee: Ben Kietzman
> Priority: Major
> Labels: dataset
>
> dictionary_encode should be usable in the context of ExecuteScalarExpression,
> but is not currently supported because it requires mutable state (the hash
> table). Currently scanning assumes that Expression state will not be mutated
> so only one instance is initialized and is shared between all threads of
> execution. Supporting dictionary_encode will require adding support for
> multiple states to Expression and usage of that by dataset scans.
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