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https://issues.apache.org/jira/browse/ARROW-255?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Julien Le Dem reassigned ARROW-255:
-----------------------------------
Assignee: Julien Le Dem
> Finalize Dictionary representation
> ----------------------------------
>
> Key: ARROW-255
> URL: https://issues.apache.org/jira/browse/ARROW-255
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Format
> Reporter: Julien Le Dem
> Assignee: Julien Le Dem
>
> format/Messages.fbs mentions DictionaryBatches with an id but does not
> specify where they are referenced.
> We should add a {{dictionary: long}} in Field that references the dictionary
> id:
> Field:
> https://github.com/apache/arrow/blob/34e7f48cb71428c4d78cf00d8fdf0045532d6607/format/Message.fbs#L86
> Dictionary id:
> https://github.com/apache/arrow/blob/34e7f48cb71428c4d78cf00d8fdf0045532d6607/format/Message.fbs#L165
> We need a spec in format/Layout.md that describes the dictionary layout.
> When dictionary encoded the value vector is an array of signed int32 (for
> consistency with variable length collection offsets).
> The dictionary vector is a Vector of the type of the value. indexed by their
> id in the dictionary.
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