Scala: Merge map

Question

How can I merge maps like below:

Map1 = Map(1 -> Class1(1), 2 -> Class1(2)) Map2 = Map(2 -> Class2(1), 3 -> Class2(2)) 

After merged.

Merged = Map( 1 -> List(Class1(1)), 2 -> List(Class1(2), Class2(1)), 3 -> Class2(2)) 

Can be List, Set or any other collection who has size attribute.

Answer 1

Using the standard lib, you can do it as follows:

// convert maps to seq, to keep duplicate keys and concat val merged = Map(1 -> 2).toSeq ++ Map(1 -> 4).toSeq // merged: Seq[(Int, Int)] = ArrayBuffer((1,2), (1,4))  // group by key val grouped = merged.groupBy(_._1) // grouped: scala.collection.immutable.Map[Int,Seq[(Int, Int)]] = Map(1 -> ArrayBuffer((1,2), (1,4)))   // remove key from value set and convert to list val cleaned = grouped.mapValues(_.map(_._2).toList) // cleaned: scala.collection.immutable.Map[Int,List[Int]] = Map(1 -> List(2, 4))