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https://issues.apache.org/jira/browse/ARROW-18265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17637292#comment-17637292
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Joris Van den Bossche commented on ARROW-18265:
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[~westonpace] one aspect to explicitly call out: are we OK with the fact that
an integer index element in a FieldPath _means_ a "list element" selection? (or
would you prefer to implement this differently?)
Because if we decide that an index means "list element selection" for
ListTypes, that also means we can't use that to "select" the full (single)
child field of a ListType. Mentioning this because you used {{field_ref(0)}} /
{{field_ref("item")}} example as one option in
https://issues.apache.org/jira/browse/ARROW-17820 how to reference the child
field (for expresssion you want to apply an element-wise kernel on the child
array of a ListArray).
> [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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