collection2string.scala

val list = List(1, 2, 3)                        //> list  : List[Int] = List(1, 2, 3)
list.map(_.toString).mkString(", ")             //> res0: String = 1, 2, 3

val map = Map(1 -> "A", 2 -> "B", 3 -> "C")     //> map  : scala.collection.immutable.Map[Int,String] = Map(1 -> A, 2 -> B, 3 -> C)
map.map(_ match { case (k, v) => k + ":" + v }).mkString(", ")
                                                //> res1: String = 1:A, 2:B, 3:C