What’s a good and functional way to swap collection elem ents in Scala?

Andreas Eisele skrev 2010-07-26 16:22:
> In a project of mine one common use case keeps coming up. At some point
> I've got a sorted collection of some kind (List, Seq, etc... doesn't
> matter) and one element of this collection. What I want to do is to swap
> the given element with it's following element (if this element exists) or
> at some times with the preceding element.
>
> I'm well aware of the ways to achieve this using procedural programming
> techniques. My question is what would be a good way to solve the problem
> by means of functional programming (in Scala)?

def swapElems[T](s : Seq[T], elem : T, before : Boolean) = {
val i = s.indexOf(elem)

if (before)
s.patch(i - 1, elem :: s(i - 1) :: Nil, 2)
else
s.patch(i, s(i + 1) :: elem :: Nil, 2)
}

/Jesper Nordenberg