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

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

Wes McKinney created ARROW-608:
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             Summary: [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 C++-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 C++-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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