Calculating differences of subsequent elements of a sequence in scala

Question

I would like to do almost exactly this in scala. Is there an elegant way?

Specifically, I just want the difference of adjacent elements in a sequence. For example

input = 1,2,6,9
output = 1,4,3

Answer 1

How about this?

scala> List(1, 2, 6, 9).sliding(2).map { case Seq(x, y, _*) => y - x }.toList
res0: List[Int] = List(1, 4, 3)

Answer 2

Here is one that uses recursion and works best on Lists

def differences(l:List[Int]) : List[Int] = l match {
  case a :: (rest @ b :: _) => (b - a) :: differences(rest)
  case _ => Nil
}

And here is one that should be pretty fast on Vector or Array:

def differences(a:IndexedSeq[Int]) : IndexedSeq[Int] = 
  a.indices.tail.map(i => a(i) - a(i-1))

Of course there is always this:

def differences(a:Seq[Int]) : Seq[Int] = 
  a.tail.zip(a).map { case (x,y) => x - y }

Note that only the recursive version handles empty lists without an exception.