LetterCounter.scala

object LetterCounter extends App{
    val filters = args.lift(1).getOrElse("aeiou").toList
    val grouped = args(0).groupBy(l=>l).collect{case (l,g) => (l, g.length)}
    val groupCount = filters.map(v => grouped.find(x=> x._1==v).getOrElse((v,0)))
    val output = groupCount.foldLeft("")((result, pair) => result+pair._1 + ": "+pair._2+" ")

    println(output)
}