CODEWITHSUNDEEP
scalacollections
elm
elm

Reputation: 20415

In Scala, apply function to values for some keys in immutable map

Let an immutable map 

val m = (0 to 3).map {x => (x,x*10) }.toMap
m: scala.collection.immutable.Map[Int,Int] = Map(0 -> 0, 1 -> 10, 2 -> 20, 3 -> 30)

a collection of keys of interest

val k = Set(0,2)

and a function 

def f(i:Int) = i + 1

How to apply f onto the values in the map mapped by the keys of interest so that the resulting map would be

Map(0 -> 1, 1 -> 10, 2 -> 21, 3 -> 30)

Upvotes: 4

Views: 2815

Answers (3)

LRLucena
LRLucena

Reputation: 1705

A variation of @regis-jean-gilles answer using map and pattern matching

m.map { case a @ (key, value) => if (k(key)) key -> f(value) else a }

Upvotes: 0

Régis Jean-Gilles
Régis Jean-Gilles

Reputation: 32719

m.transform{ (key, value) => if (k(key)) f(value) else value }

Upvotes: 6

goral
goral

Reputation: 1265

That's the first thing that popped into my mind but I am pretty sure that in Scala you could do it prettier:

m.map(e =>  {
    if(k.contains(e._1)) (e._1 -> f(e._2)) else (e._1 -> e._2)
})

Upvotes: 1

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