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https://issues.apache.org/jira/browse/ARROW-18265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17641982#comment-17641982
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Joris Van den Bossche commented on ARROW-18265:
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bq. However, it would be a bit tricky if FindOne/FindAll ended up calling
list_element (a compute function). FindOne/FindAll currently is in the core
module and not the compute module.
That's a good point. So, for doing FindOne/FindAll itself, we won't need
"list_element" kernel, since this returns a path, and for that we don't need to
do the actual selection from the array.
There is however a set of {{FieldPath::Get(..)}} methods that you can call on
the resulting FieldPath. For "getting" the path from a schema or type, that's
still OK (no need for the actual kernel), but there is a signature for
{{Get()}} to apply the path on a record batch or array. For that specific case,
one would actually need to use the kernel. Now, I am not sure we actually use
this variant internally, though (outside of a few tests).
> [C++] Allow FieldPath to work with ListElement
> ----------------------------------------------
>
> Key: ARROW-18265
> URL: https://issues.apache.org/jira/browse/ARROW-18265
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Miles Granger
> Assignee: Miles Granger
> Priority: Major
> Labels: pull-request-available
> Fix For: 11.0.0
>
> Time Spent: 1h 40m
> Remaining Estimate: 0h
>
> {{FieldRef::FromDotPath}} can parse a single list element field. ie.
> {{{}'path.to.list[0]`{}}}but does not work in practice. Failing with:
> _struct_field: cannot subscript field of type list<....>_
> Being able to add a slice or multiple list elements is not within the scope
> of this issue.
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