Question

I have iterator with a lot of items so I can’t convert it to Iterable for groupBy and don’t want to sotre all results in memmory.
But I know that all object are ordered by groupBy field so it seems possible to implement groupBy for sorted iterators… Is there already some method in scala collection to do this?

Answer 1

My solution:

 def iterativeGroupBy[T, B](iterO: Iterator[T])(func: T => B): Iterator[List[T]] = new Iterator[List[T]] {
    var iter = iterO
    def hasNext = iter.hasNext

    def next = {
      val first = iter.next()
      val firstValue = func(first)
      val (i1,i2) = iter.span(el => func(el) == firstValue)
      iter = i2
      first :: i1.toList
    }
  }