CODEWITHSUNDEEP
listscaladictionary
eceppda
eceppda

Reputation: 237

Scala - Map A Tuple To A Map of Maps?

I have a list of tuples:

val t = List( (1,2,1.0), (1,3,2.0), (1,2,1.1) )

I want to create a map with t._1 as the key, and as the value a map with t._2 as the key and the sum of t._3 as the value.

val m = Map( (1-> Map((2 -> 2.1), (3 -> 2.0)) )

How can I do this in Scala?

I'd like to accomplish this with pure Scala as opposed to a library, but if a library such as scalaz etc. is (in my completely subjective opinion) a nicer looking solution, I would accept that answer as well.

Upvotes: 3

Views: 268

Answers (2)

marios
marios

Reputation: 8996

If you are into one-liners then you might like this:

val t = List( (1,2,1.0), (1,3,2.0), (1,2,1.1) )
t.groupBy(_._1).mapValues(_.groupBy(_._2).mapValues(_.map(_._3).sum))

Result is:

Map(1 -> Map(2 -> 2.1, 3 -> 2.0))

Upvotes: 6

heenenee
heenenee

Reputation: 20145

Here's one way:

t.groupBy(_._1).map {
    case (outerKey, outerList) =>
        outerKey -> outerList.groupBy(_._2).map {
            case (innerKey, innerList) =>
                innerKey -> innerList.map(_._3).sum
        }
}

yields:

Map(1 -> Map(2 -> 2.1, 3 -> 2.0))

Upvotes: 2

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