Ian Cook created ARROW-13186:
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Summary: [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
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}}s.
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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