Julien Le Dem created ARROW-255:
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Summary: 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
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 unsigned int32.
The dictionary vector is a Vector of the type of the value. indexed by their id
in the dictionary.
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