First off, some thoughts:
// You should use `val` instead of `var`
var matches: List[Tuple2[String, Int]] = List("a" -> 1, "a" -> 2, "b" -> 3, "c" -> 4, "c" -> 5)
var m = matches
.toSeq // This isn't necessary: it's already a Seq
.groupBy(i => i._1)
.map(t => (t._1, t._2)) // This isn't doing anything at all
.toSeq
.sortWith(_._2.size > _._2.size) // `sortBy` will reduce redundancy
.sortWith(_._2.size > _._2.size) // Not sure why you have this twice since clearly the
// second sorting isn't doing anything...
So try this:
val matches: List[Tuple2[String, Int]] = List("a" -> 1, "a" -> 2, "b" -> 3, "c" -> 4, "c" -> 5)
val m: Seq[(String, Seq[Int])] =
matches
.groupBy(_._1)
.map { case (k, vs) => k -> vs.map(_._2) } // Drop the String part of the value
.toVector
.sortBy(_._2.size)
println(m) // Vector((b,List(3)), (a,List(1, 2)), (c,List(4, 5)))