How to sum a list of tuples - scala

Question

Given the following list of tuples...
val list = List((1, 2), (1, 2), (1, 2))
... how do I sum all the values and obtain a single tuple like this?
(3, 6)

Answer 1

Using the foldLeft method. Please look at the scaladoc for more information.
scala> val list = List((1, 2), (1, 2), (1, 2))
list: List[(Int, Int)] = List((1,2), (1,2), (1,2))
scala> list.foldLeft((0, 0)) { case ((accA, accB), (a, b)) => (accA + a, accB + b) }
res0: (Int, Int) = (3,6)
Using unzip. Not as efficient as the above solution. Perhaps more readable.
scala> list.unzip match { case (l1, l2) => (l1.sum, l2.sum) }
res1: (Int, Int) = (3,6)

Answer 2

Very easy: (list.map(_._1).sum, list.map(_._2).sum).

Answer 3

You can solve this using Monoid.combineAll from the cats library:
import cats.instances.int._ // For monoid instances for `Int`
import cats.instances.tuple._ // for Monoid instance for `Tuple2`
import cats.Monoid.combineAll
def main(args: Array[String]): Unit = {
val list = List((1, 2), (1, 2), (1, 2))
val res = combineAll(list)
println(res)
// Displays
// (3, 6)
}
You can see more about this in the cats documentation or Scala with Cats.

Answer 4

answering to this question while trying to understand aggregate function in spark
scala> val list = List((1, 2), (1, 2), (1, 2))
list: List[(Int, Int)] = List((1,2), (1,2), (1,2))
scala> list.aggregate((0,0))((x,y)=>((y._1+x._1),(x._2+y._2)),(x,y)=>(x._1+y._2,y._2+x._2))
res89: (Int, Int) = (3,6)
Here is the link to the SO QA that helped to understand and answer this [Explain the aggregate functionality in Spark

Answer 5

Scalaz solution (suggestied by Travis and for some reason a deleted answer):
import scalaz._
import Scalaz._
val list = List((1, 2), (1, 2), (1, 2))
list.suml
which outputs
res0: (Int, Int) = (3,6)

Answer 6

You can also use a reduce function :
val list = List((1, 2), (1, 2), (1, 2))
val res = list.reduce((x, y) => (x._1 + y._1, x._2 + y._2))