Scala: Filtering based on type

Question

I\'m learning Scala as it fits my needs well but I am finding it hard to structure code elegantly. I\'m in a situation where I have a List x and wa

Answer 1

Use list.partition:

scala> val l = List(1, 2, 3)
l: List[Int] = List(1, 2, 3)

scala> val (even, odd) = l partition { _ % 2 == 0 }
even: List[Int] = List(2)
odd: List[Int] = List(1, 3)

EDIT

For partitioning by type, use this method:

def partitionByType[X, A <: X](list: List[X], typ: Class[A]): 
    Pair[List[A], List[X]] = {
    val as = new ListBuffer[A]
    val notAs = new ListBuffer[X]
    list foreach {x =>
      if (typ.isAssignableFrom(x.asInstanceOf[AnyRef].getClass)) {
        as += typ cast x 
      } else {
        notAs += x
      }
    }
    (as.toList, notAs.toList)
}

Usage:

scala> val (a, b) = partitionByType(List(1, 2, "three"), classOf[java.lang.Integer])
a: List[java.lang.Integer] = List(1, 2)
b: List[Any] = List(three)