akka Akka Streams Akka-Streams: subflows
Example
You can dynamically fork a flow in multiple subflows using groupBy. The continuing stages are applied to each subflow until you merge them back using mergeSubstreams.
val sumByKey: Flow[(String, Int), Int, NotUsed] =
Flow[(String, Int)].
groupBy(Int.maxValue, _._1). //forks the flow
map(_._2). //this is applied to each subflow
fold(0)(_ + _).
mergeSubstreams //the subflow outputs are merged back together
