How to access Tuples of a List in a Map in Scala?

Question

I have a map of format

scala.collection.mutable.Map[String,List[(Int, Int, Int)]]

and I want to be able to access the individual Int's. The format of the data to go in the Map will always be

Mon-18-June-2018,1:10:5,2:20:10,3:30:15,4:40:20,5:50:25

Where the date is the key of the Map and each set of three numbers is the (Int, Int, Int)

So far, I have been able to print the Map in this format

Mon-18-June-2018
List((1,10,5), (2,20,10), (3,30,15), (4,40,20), (5,50,25))

Using the below code

map.keys.foreach{i =>
    println(i)
    println(map(i))

I would like to be able to access the individual values in the tuples. For example, I would like to be able to add every 2nd and 3rd value of each tuple together
(1,10,5)
(2,20,10)
(3,30,15)
(4,40,20)
(5,50,25)

to get
(6,150,75)

How do I do this?

How does adding the second and third value result in (6,150,75)? Where does the 6 come from? — James Whiteley, Apr 09 '19 at 08:12
Possible duplicate of [Scala: How to sum a list of tuples](https://stackoverflow.com/questions/30154736/scala-how-to-sum-a-list-of-tuples) — James Whiteley, Apr 09 '19 at 10:32

score 4 · Answer 1 · answered Apr 09 '19 at 08:17

You can use pattern matching to access elements of the tuple.

val dateMap :Map[String,List[(Int, Int, Int)]] =
  Map("Mon-18-June-2018" ->
    List((1,10,5), (2,20,10), (3,30,15), (4,40,20), (5,50,25)))

dateMap.values.map(_.fold((1,0,0)){case ((a,b,c),(x,y,z)) => (a+1,b+y,c+z)})
//res0: Iterable[(Int, Int, Int)] = List((6,150,75))

Pablo López Gallego · Answer 2 · 2019-04-10T09:55:46.017

2

The easiest way is:

val yourMap : Map[String,List[(Int, Int, Int)]] = Map("Mon-18-June-2018" -> List((1,10,5), (2,20,10), (3,30,15), (4,40,20), (5,50,25)))
yourMap.map(x=> (x._2.length+1,x._2.map(_._2).sum,x._2.map(_._3).sum))

you can find more forms here: Scala: How to sum a list of tuples

edited Apr 10 '19 at 09:55

answered Apr 09 '19 at 08:22

Pablo López Gallego

690
4
16

score 1 · Accepted Answer · answered Apr 09 '19 at 08:19

To get each individual value in a List, you could .map inside it.

To get each element of a Tuple, use tuple._1, tuple._2, tuple._3, and so on.

In your case, to add all of the values of the Tuples together you can do something like this:

val m = scala.collection.mutable.Map[String,List[(Int, Int, Int)]](
  "Mon-18-June-2018" -> List((1, 10, 5), (2, 20, 10), (3, 30, 15), (4, 40, 20), (5, 50, 25))
)

m.map {
  // get keys and values
  case (k, v) =>
    // construct a Tuple of all of the sums
    (v.map(_._1).sum, v.map(_._2).sum, v.map(_._3).sum)
}
// ArrayBuffer((15,150,75))

This will create a List of Tuples ((Int, Int, Int)), where each Tuple corresponds to a key in the original Map. You could even keep the original Map's keys by doing something like this:

m.map{
  // get keys and values
  case (k, v) =>
    // "x -> y" creates a Tuple, or in this case a Map
    k -> (v.map(_._1).sum, v.map(_._2).sum, v.map(_._3).sum)
}
// Map(Mon-18-June-2018 -> (15,150,75))

As I commented on the question, it was never explained how OP got 6 for the first Tuple value in the first place. I assumed it was a typo. How do you suggest they expected to get 6? — James Whiteley, Apr 10 '19 at 10:03

How to access Tuples of a List in a Map in Scala?

3 Answers3