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https://issues.apache.org/jira/browse/ARROW-6184?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Micah Kornfield resolved ARROW-6184.
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Fix Version/s: 1.0.0
Resolution: Fixed
Issue resolved by pull request 5058
[https://github.com/apache/arrow/pull/5058]
> [Java] Provide hash table based dictionary encoder
> --------------------------------------------------
>
> Key: ARROW-6184
> URL: https://issues.apache.org/jira/browse/ARROW-6184
> Project: Apache Arrow
> Issue Type: New Feature
> Components: Java
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.0.0
>
> Time Spent: 5h
> Remaining Estimate: 0h
>
> This is the second part of ARROW-5917. We provide a sort based encoder, as
> well as a hash table based encoder, to solve the problem with the current
> dictionary encoder.
> In particular, we solve the following problems with the current encoder:
> # There are repeated conversions between Java objects and bytes (e.g.
> vector.getObject(i)).
> # Unnecessary memory copy (the vector data must be copied to the hash table).
> # The hash table cannot be reused for encoding multiple vectors (other data
> structure & results cannot be reused either).
> # The output vector should not be created/managed by the encoder (just like
> in the out-of-place sorter)
> # The hash table requires that the hashCode & equals methods be implemented
> appropriately, but this is not guaranteed.
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