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Posted to issues@arrow.apache.org by "Wes McKinney (JIRA)" <ji...@apache.org> on 2019/06/11 20:23:00 UTC
[jira] [Commented] (ARROW-2428) [Python] Add API to map Arrow types (including extension types) to pandas ExtensionArray instances for to_pandas conversions
[ https://issues.apache.org/jira/browse/ARROW-2428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16861462#comment-16861462 ]
Wes McKinney commented on ARROW-2428:
-------------------------------------
I just updated the title to reflect the updated scope of handling general Arrow-to-ExtensionArray mappings, including the new C++ ExtensionType facility
> [Python] Add API to map Arrow types (including extension types) to pandas ExtensionArray instances for to_pandas conversions
> ----------------------------------------------------------------------------------------------------------------------------
>
> Key: ARROW-2428
> URL: https://issues.apache.org/jira/browse/ARROW-2428
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Python
> Reporter: Uwe L. Korn
> Priority: Major
> Fix For: 1.0.0
>
>
> With the next release of Pandas, it will be possible to define custom column types that back a {{pandas.Series}}. Thus we will not be able to cover all possible column types in the {{to_pandas}} conversion by default as we won't be aware of all extension arrays.
> To enable users to create {{ExtensionArray}} instances from Arrow columns in the {{to_pandas}} conversion, we should provide a hook in the {{to_pandas}} call where they can overload the default conversion routines with the ones that produce their {{ExtensionArray}} instances.
> This should avoid additional copies in the case where we would nowadays first convert the Arrow column into a default Pandas column (probably of object type) and the user would afterwards convert it to a more efficient {{ExtensionArray}}. This hook here will be especially useful when you build {{ExtensionArrays}} where the storage is backed by Arrow.
> The meta-issue that tracks the implementation inside of Pandas is: https://github.com/pandas-dev/pandas/issues/19696
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