I have a two lists, a List[A] and a List[B]. What I want is a Map[A,B] but I want the semantics of zip. So started out like so:
var tuplesOfAB = listOfA zip listOfB
Now I'm not sure how to construct a Map from my tuplesOfAB.
As a follow-up question, I also want to invert my map so that from a Map[A,B] I can create a Map[B,A]. Can anyone hit me with a clue-stick?
In 2.8 this is really simple using the CanBuildFrom functionality (as described by Daniel) and using breakOut with a type instruction to the compiler as to what the result type should be:
import scala.collection.breakOut
val m = (listA zip listB)(breakOut): Map[A,B]
The following would also work:
val n: Map[A,B] = (listA zip listB)(breakOut)
And (as EastSun, below, has pointed out) this has been added to the library as toMap
val o = (listA zip listB).toMap
As for reversing the map, you can do:
val r = m.map(_.swap)(breakOut): Map[B, A]
Now that you've got a list of tuples it is easy to make it into a map by writing Map(tuplesOfAB: _*). The : _* notation means to call the varargs overload with the arguments taken from the sequence. This seems like a funny bit of syntax, but it helps to think that varargs are declared like Map[A,B](pairs: (A,B)*) and the : _* is a type annotation to convert to varargs because of the common * part.
To reverse a map m use Map(m.map(_.swap): _*). In scala a map is also a collection of pairs. This transforms those pairs by swapping the elements and passing them to the Map constructor.