Scala: Producing the intermediate results of a fold

Question

I\'ve come across the problem of maintaining a state throughout a map operation several times. Imagine the following task:

Given a List[Int], map each element to the

Answer 1

The scan answers are the best ones, but it's worth noting that one can make the fold look nicer and/or be shorter than in your question. First, you don't need to use pattern matching:

a.foldLeft(List(0)){ (l,i) => (l.head + i) :: l }.reverse

Second, note that foldLeft has an abbreviation:

(List(0) /: a){ (l,i) => (l.head + i) :: l }.reverse

Third, note that you can, if you want, use a collection that can append efficiently so that you don't need to reverse:

(Vector(0) /: a){ (v,i) => v :+ (v.last + i) }

So while this isn't nearly as compact as scanLeft:

a.scanLeft(0)(_ + _)

it's still not too bad.