Explanation of the aggregate scala function

Question

I do not get to understand yet the aggregate function:

For example, having:

val x = List(1,2,3,4,5,6)
val y = x.par.aggregate((0, 0))((x, y) => (x._1          


        

Answer 1

Adding to Rashmit answer.

• CombOp is called only if the collection is processed in parallel mode.

See below example :

val listP: ParSeq[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).par

val aggregateOp1 = listP.aggregate[String]("Aggregate-")((a, b) => a + b, (s1, s2) => {
  println("Combiner called , if collections is processed parallel mode")
  s1 + "," + s2
})
println(aggregateOp1)

OP : Aggregate-1,Aggregate-2,Aggregate-3,Aggregate-45,Aggregate-6,Aggregate-7,Aggregate-8,Aggregate-910

val list: Seq[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

val aggregateOp2 = list.aggregate[String]("Aggregate-")((a, b) => a + b, (s1, s2) => {
  println("Combiner called , if collections is processed parallel mode")
  s1 + "," + s2
})
println(aggregateOp2)

}

OP : Aggregate-12345678910

In above example, combiner operation is called only if collection is operated in parallel