Scala Map conversion

Question

I'm a Scala newbie I'm afraid: I'm trying to convert a Map to a new Map based on some simple logic:

val postVals = Map("test" -> "testing1", "test2" -> "testing2", "test3" -> "testing3")

I want to test for value "testing1" and change the value (while creating a new Map)

def modMap(postVals: Map[String, String]): Map[String, String] = {
                    postVals foreach {case(k, v) => if(v=="testing1") postVals.update(k, "new value")}
                    }

Answer 1

You could use the 'map' method. That returns a new collection by applying the given function to all elements of it:

scala> def modMap(postVals: Map[String, String]): Map[String, String] = {
   postVals map {case(k, v) => if(v == "a") (k -> "other value") else (k ->v)}
}

scala> val m = Map[String, String]("1" -> "a", "2" -> "b")
m: scala.collection.immutable.Map[String,String] = Map((1,a), (2,b))

scala> modMap(m)
res1: Map[String,String] = Map((1,other value), (2,b))

Answer 2

Alternative to Arjan's answer: (just a slight change)

scala> val someMap = Map("a" -> "apple", "b" -> "banana")
someMap: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map(a -> apple, b -> banana)

scala> val newMap = someMap map {                                     
     |   case(k , v @ "apple") => (k, "alligator")            
     |   case pair             => pair            
     | }
newMap: scala.collection.immutable.Map[java.lang.String,java.lang.String] = Map(a -> alligator, b -> banana)

Answer 3

Just add an updating pair with the plus-sign:

val someMap = Map ("a" -> "apple", "b" -> "banana")
val upd = someMap + ("a" -> "ananas")