Feat: Implement idempotent array reducer

[guidiaz]

So multi-dimensional retrievals can be composed as an array of sources, and data arrays overstep to tally phase, where a mode array reducer may be applied there (for instance).

[aesedepece]

@guidiaz can you elaborate? Maybe some examples may help me understand what you mean :thinking:

[tmpolaczyk]

I think it refers to an identity reducer that can do [T] => [T], to be used in the aggregation stage. The use case would be to get different kinds of data using a single data request.

[aesedepece]

I think it refers to an identity reducer that can do [T] => [T], to be used in the aggregation stage. The use case would be to get different kinds of data using a single data request.

Oh I see. You can opt out from filters at the aggregation stage, but not from reducers.

This is a tricky one, because [T] => T is the very signature of the aggregation stage.

Very interesting.