Merge objects in mutable list on Scala

Question

I have recently started looking at Scala code and I am trying to understand how to go about a problem.

I have a mutable list of objects, these objects have an id: String and values: List[Int]. The way I get the data, more than one object can have the same id. I am trying to merge the items in the list, so if for example, I have 3 objects with id 123 and whichever values, I end up with just one object with the id, and the values of the 3 combined.

I could do this the java way, iterating, and so on, but I was wondering if there is an easier Scala-specific way of going about this?