Idiomatic way to update value in a Map based on previous value

Question

Let\'s say I store bank accounts information in an immutable Map:

val m = Map(\"Mark\" -> 100, \"Jonathan\" -> 350, \"Bob\" -> 65)
         


        

Answer 1

An SO Answer proposes another alternative, using the |+| operator from scalaz

val m2 = m |+| Map("Mark" -> -50)

The |+| operator will sum the values of an existing key, or insert the value under a new key.