[ARROW-15735] [C++] Hash aggregate functions to return first and last value from a group.

• Type: New Feature
• Status: In Progress
• Priority: Major
• Resolution: Unresolved
• Component/s: C++
• Labels: kernel pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/31183
• Assignee: Sanjiban Sengupta
• Reporter: A. Coady
• Created: 20/Feb/22 22:48
• Updated: 11/Jan/23 11:39

Description

Follow-up to ARROW-13993, which implemented `hash_one` to select an arbitrary value, as the core engine lack support for ordering. I think `first` and `last` will still be in demand though, based on pandas and sql usage.

It could be done without core changes by using `min_max` on an array of indices. For that reason, maybe it would be better as `hash_{first,last}_index`, suitable for use with `take`.

Issue Links

• links to: GitHub Pull Request #15159