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https://issues.apache.org/jira/browse/ARROW-13186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17369622#comment-17369622
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Ian Cook commented on ARROW-13186:
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Nice, thanks [~npr].
Yes, using {{eval_select}} across the board is ARROW-12105. I hope to get that
done for 5.0.0.
> [R] Implement type determination more cleanly
> ---------------------------------------------
>
> Key: ARROW-13186
> URL: https://issues.apache.org/jira/browse/ARROW-13186
> Project: Apache Arrow
> Issue Type: Improvement
> Components: R
> Affects Versions: 5.0.0
> Reporter: Ian Cook
> Priority: Major
>
> In the R package, there are several improvements in data type determination
> in the 5.0.0 release. The implementation of these improvements used a kludge:
> They made it possible to store a {{Schema}} in an {{Expression}} object in
> the R package; when set, this {{Schema}} is retained in derivative
> {{Expression}} objects. This was the most convenient way to make the
> {{Schema}} available for passing it to the {{type_id()}} method, which
> requires it. But this introduces a deviation of the R package's
> {{Expression}} object from the C++ library's {{Expression}} object, and it
> makes our type determination functions work differently than the other R
> functions in {{nse_funcs}}.
> The Jira issues in which these somewhat kludgy improvements were made are:
> * allowing a schema to be stored in the {{Expression}} object, and
> implementing type determination functions in a way that uses that schema
> (ARROW-12781)
> * retaining a schema in derivative {{Expression}} objects (ARROW-13117)
> * setting an empty schema in scalar literal {{Expression}} objects
> (ARROW-13119)
> From the perspective of the R package, an ideal way to implement type
> determination functions would be to call a {{type_id}} kernel through the
> {{call_function}} interface, but this was rejected in ARROW-13167. Consider
> other ways that we might improve this implementation.
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