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https://issues.apache.org/jira/browse/ARROW-2428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16943671#comment-16943671
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Joris Van den Bossche commented on ARROW-2428:
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More thoughts on this?
I implemented a POC for case 1 described above in
https://github.com/apache/arrow/pull/5512
This allows to roundtrip pandas ExtensionArrays, assuming the the
pandas.ExtensionDtype implements a {{\_\_from_arrow\_\_}} to convert an Arrow
array into a pandas ExtensionArray of that dtype (so it can be put in the
resulting DataFrame as an extension array).
It doesn't yet handle to other cases described above, though.
> [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 Korn
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.0.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> 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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