[jira] [Commented] (ARROW-608) [Format] Days since epoch date type

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

    [ https://issues.apache.org/jira/browse/ARROW-608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15906840#comment-15906840 ] 

Wes McKinney commented on ARROW-608:
------------------------------------

[~julienledem] I linked with ARROW-316

> [Format] Days since epoch date type
> -----------------------------------
>
>                 Key: ARROW-608
>                 URL: https://issues.apache.org/jira/browse/ARROW-608
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: Format
>            Reporter: Wes McKinney
>
> While we've decided to make the primary IPC date type be int64 milliseconds since the UNIX epoch, in many libraries dates are represented as integer (int32, usually) days since some epoch. In the Python standard library, the epoch is the year 0:
> {code}
> >>> d = datetime.date(2017, 1, 17)
> >>> d.toordinal()
> 736346
> >>> d.toordinal() / 365
> 2017
> {code}
> At least in Cplusplus-land, in working on ARROW-452 I ran into the problem of how to do zero-copy reads of such data, while preserving the metadata to know that the values are dates. I added a cpp-only "date32" type to support this use case https://github.com/apache/arrow/pull/365
> I'm not sure whether we should add a new logical type, but thought it would be worth bringing up in any case



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