Scala: what is the most appropriate data structure for sorted subsets?
val a = Vector( 9,2,6,1,7,5,2,6,9 ) // just an example
val f : (Int)=>Double = (n)=>n      // evaluation function
val b = a.sortBy( f ).take( N )     // sort, then clip

def firstK[A](xs: Seq[A], k: Int)(implicit ord: Ordering[A]) = {
  val q = new scala.collection.mutable.PriorityQueue[A]()(ord.reverse)
  val (before, after) = xs.splitAt(k)
  q ++= before
  after.foreach(x => q += ord.max(x, q.dequeue))
  q.dequeueAll
}

scala> firstK(Vector(9, 2, 6, 1, 7, 5, 2, 6, 9), 4)
res14: scala.collection.mutable.Buffer[Int] = ArrayBuffer(6, 7, 9, 9)