How to convert a Seq[A] to a Map[Int, A] using a value of A as the key in the map?

Question

I have a Seq containing objects of a class that looks like this:

class A (val key: Int, ...) 

Now I want to convert this Seq to a Map, using the key value of each object as the key, and the object itself as the value. So:

val seq: Seq[A] = ... val map: Map[Int, A] = ... // How to convert seq to map? 

How can I does this efficiently and in an elegant way in Scala 2.8?

Answer 1

Since 2.8 Scala has had .toMap, so:

val map = seq.map(a => a.key -> a).toMap 

or if you're gung ho about avoiding constructing an intermediate sequence of tuples, then in Scala 2.8 through 2.12:

val map: Map[Int, A] = seq.map(a => a.key -> a)(collection.breakOut) 

or in Scala 2.13 and 3 (which don't have breakOut, but do have a reliable .view):

val map = seq.view.map(a => a.key -> a).toMap 

Answer 2

Map over your Seq and produce a sequence of tuples. Then use those tuples to create a Map. Works in all versions of Scala.

val map = Map(seq map { a => a.key -> a }: _*)