Iterate through scala Vector and pair a certain object with the next one - scala

Question

Assuming that I have a collection (Vector[Int]),1,2,5,4,3,5,5,5,6,7,7 and want to get another collection (Vector[Vector[Int]]) pairing every number 5 with the next number (1),(2),(5,4),(3),(5,5),(5,6),(7),(7) what are my options apart from this:
var input= Vector.[Int]
var output = Vector.empty[Vector[Int]]
var skip = false
for(i <- input.indices){
if (input(i) == 5 && skip == false){
output = output :+ input(i) :+ input(i + 1)
skip = true;
}else if(input(i - 1) != 5){
output = output :+ input(i)
}else{
skip = false;
}
}
which works but is not very scala-like.
Would it be possible to achieve the same result with a for comprehension? for(x <- c; if cond) yield {...}

Answer 1

You can use foldLeft
val output = input.foldLeft (Vector.empty[Vector[Int]]) { (result, next) =>
if(!result.isEmpty && result.last == Vector(5)) {
result.dropRight(1) :+ Vector(5, next)
} else {
result :+ Vector(next)
}
}

Answer 2

You could use pattern matching as well
def prepareVector(lv: Vector[Int]): Vector[Vector[Int]] = {
val mv = new ArrayBuffer[Vector[Int]]()
def go(ll: List[Int]): Unit = ll match {
case y :: Nil => mv += Vector(y)
case 5 :: ys => {
mv += Vector(5, ys.head)
go(ys.tail)
}
case y :: ys => {
mv += Vector(y)
go(ys)
}
case Nil => None
}
go(lv.toList)
mv.toVector
}