[jira] [Commented] (ARROW-257) Add a typeids Vector to Union type

["Wes McKinney (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15420729#comment-15420729 ] 

Wes McKinney commented on ARROW-257:
------------------------------------

So if I understand correctly, support we had a union of 50 types, but only 5 of them actually occur in the data, then the typeIds would indicate the indices of the observed child types. That makes sense to me.

> Add a typeids Vector to Union type
> ----------------------------------
>
>                 Key: ARROW-257
>                 URL: https://issues.apache.org/jira/browse/ARROW-257
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: Format
>            Reporter: Julien Le Dem
>
> {noformat}
> enum UnionMode:int { Sparse, Dense }
> table Union {
>   mode: UnionMode;
>   typeIds: [Int32]; // optional, describes typeid of each child.
> }
> {noformat}
> The idea is to enable providing an id different from the child offset (the default)
> This enables an optimization where we use predefined ids when constructing the type vector of the union but want the children to be only the actually used types.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)