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https://issues.apache.org/jira/browse/ARROW-13167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17368978#comment-17368978
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Ian Cook commented on ARROW-13167:
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>From the perspective of a user of a compute API, it is quite inconvenient to
>switch to using a completely different API in order to determine the data type
>of a datum. This is a notorious gripe that SQL developers have with many
>database systems, and it's the reason why some SQL engines like
>[Snowflake|https://docs.snowflake.com/en/sql-reference/functions/typeof.html]
>and [Impala
>title|https://docs.cloudera.com/documentation/enterprise/6/6.3/topics/impala_conversion_functions.html#conversion_functions__typeof]
> have added a {{typeof()}} function to their SQL dialects. I agree that it
>feels like an "off-label" use of compute functions, but I think the utility it
>affords warrants this.
> [C++] Type determination kernels ("type", "type_id")
> ----------------------------------------------------
>
> Key: ARROW-13167
> URL: https://issues.apache.org/jira/browse/ARROW-13167
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Ian Cook
> Priority: Major
>
> The Arrow C++ library exposes an API for determining the data type of an
> expression, but it is exposed as a method of the expression class and it
> requires that the user pass a schema as an argument to the method. This is
> inconvenient; for example, we have had to write some inconsistent code in the
> R bindings to make expression objects carry schemas along with them and then
> pass the schemas to derivative expressions, unifying schemas as needed for
> derivative expressions that take 2+ expressions as arguments.
> This would be much cleaner if we could use the kernel function calling
> interface to call a unary {{type_id}} function that would simply determine
> the type of its input datum and return a scalar integer value from the data
> type enum indicating the its data type. It would be convenient to also have a
> version of this that returned the string description of the data type; I
> think this could be named {{type}}.
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