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https://issues.apache.org/jira/browse/ARROW-16288?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Li closed ARROW-16288.
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Resolution: Not A Problem
ValueDescr was simply removed.
> [C++] ValueDescr::SCALAR nearly unused and does not work for projection
> -----------------------------------------------------------------------
>
> Key: ARROW-16288
> URL: https://issues.apache.org/jira/browse/ARROW-16288
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Weston Pace
> Priority: Major
>
> First, there are almost no kernels that actually use this shape. Only the
> functions "all", "any", "list_element", "mean", "product", "struct_field",
> and "sum" have kernels with this shape. Most kernels that have special logic
> for scalars handle it by using {{ValueDescr::ANY}}
> Second, when passing an expression to the project node, the expression must
> be bound based on the dataset schema. Since the binding happens based on a
> schema (and not a batch) the function is bound to ValueDescr::ARRAY
> (https://github.com/apache/arrow/blob/a16be6b7b6c8271202ff766b99c199b2e29bdfa8/cpp/src/arrow/compute/exec/expression.cc#L461)
> This results in an error if the function has only ValueDescr::SCALAR kernels
> and would likely be a problem even if the function had both types of kernels
> because it would get bound to the wrong kernel.
> This simplest fix may be to just get rid of ValueDescr and change all kernels
> to ValueDescr::ANY behavior. If we choose to keep it we will need to figure
> out how to handle this kind of binding.
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