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Add IterableOps.groupFlatMap method #135
Description
We already have IterableOps.groupMap and groupMapReduce methods, does it make sense to add a groupFlatMap method as well?
In the simplest case this could just be an alias for groupMapReduce(f)(g)(_ ++ _) but if implemented separately it can be more efficient:
- we can avoid an extra function call to the reducer "wrapper" function for each element
- we can use a mutable buffer internally to build up the list of values
Indeed groupMapReduce already states in its doc that it exists (solely?) because it's more efficient than rolling the behaviour by hand using groupBy(f).map(...). It also somehow "feels" like this is missing from the API since we generally expect map and flatMap to come as a pair.
Activity
BalmungSan commentedon Oct 17, 2022
It could be added as part of my proposal here: #53
[-]Add `Iterable.groupFlatMap` method[/-][+]Add `IterableOps.groupFlatMap` method[/+]ashleymercer commentedon Oct 17, 2022
@BalmungSan looks like there's some overlap of ideas here, but your proposal is more complex since you're changing the target type of collection. I would expect
groupFlatMapto be much simpler - I already have a draft implementation which I'm using locally - so hopefully much easier to get it accepted / merged.For example, I'd expect to keep the existing behaviour of
flatMapthat you end up with the source type of collection, for example:The resulting type is
bs: Seq[Int]rather thanbs: List[Int], so I'd expectgroupFlatMapto behave similarly (and obviously changing this for regularflatMapwould be a whole separate discussion).Of course, at some point you could propose adding
groupFlatMapToas well :)(Also updated issue title and description to reflect the fact that this should really live on
IterableOps, not onIterable)