[jira] [Created] (ARROW-13186) [R] Implement type determination more cleanly

["Ian Cook (Jira)" <ji...@apache.org>]

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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