[FEA]: DeviceReduceTransformReduceByKey

[AustinSchuh]

Is this a duplicate?

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Area

CUB

Is your feature request related to a problem? Please describe.

I'm trying to use DeviceReduce to efficiently compute the bounding box for each set of inputs which have a matching key. The input value is a lot smaller than the structure I'm reducing over.

Describe the solution you'd like

I would like to see the ByKey equivalent of DeviceReduce::TransformReduce.
I'm able to do this by using a TransformInputIterator, but that consumes more memory.

Describe alternatives you've considered

DeviceReduce::ReduceByKey can be persuaded to work with a cub::TransformInputIterator, but has the same tradeoffs that made it worth building DeviceReduce::TransformReduce.

Additional context

No response