How to combine `count` and `sum` computations for the same source - scala

Question

There is a some stream of integers:
val source = Source(List(1,2,3,4,5))
Is there possible to get the (count, sum) result from the source? For the above example it will be (5, 15).
I guess I should use flows and combine them:
val countFlow = Flow[Int].fold(0)((c, _) => c + 1)
val sumFlow = Flow[Int].fold(0)((s, e) => s + e)
How to apply the above flows to the source. Or is there another way?

Answer 1

Final Total
The Flow that you presented is almost correct for getting a final value after the source is exhausted:
case class Data(sum : Int = 0, count : Int = 0)
val updateData : (Data, Int) => Data =
(data, i) => Data(data.sum + i, data.count + 1)
val zeroData = Data()
val countAndSum = Flow[Int].fold(zeroData)(updateData)
This Flow can then be combined with a Sink.head to get the final result:
val result : Future[Data] =
source
.via(countAndSum)
.runWith(Sink[Data].head)
Intermediate Values
If you want a "running counter", e.g. you want all of the intermediate Data values, then you can use Flow.scan instead of fold:
val intermediateCountAndSum =
Flow[Int].scan(zeroData)(updateData)
And you can "drain" these Data values into a Sink.seq:
val intermediateResult : Future[Seq[Data]] =
source
.via(intermediateCountAndSum)
.runWith(Sink[Data].seq)

Answer 2

val graph = Source.fromGraph(GraphDSL.create() { implicit builder =>
import GraphDSL.Implicits._
val fanOut = builder.add(Broadcast[Int](2))
val merge = builder.add(Zip[Int, Int])
source ~> fanOut ~> countFlow ~> merge.in0
fanOut ~> sumFlow ~> merge.in1
SourceShape(merge.out)
})
graph.runWith(Sink.last)

Answer 3

You can simply do the following
source.map(list => (list.length, list.reduceLeft(_+_)))
I hope its helpful

Answer 4

case class Stats(sum: Int, count: Int) {
def add(el: Int): Stats = this.copy(sum = sum += el, count = count +=1)
}
object Stats {
def empty: Stats = Stats(0, 0)
}
val countFlow = Flow[Status].fold(Stats.empty)((stats, e) => stats add e)