Question

Suppose I have a function f(n:Int):Option[String]. I would like to find such 1 <= k <= 10 that f(k) is not None. I can code it as follows:

(1 to 10).find(k => f(k).isDefined)

Now I would like to know both k and f(k).

val k = (1 to 10).find(f(_).isDefined)
val s = f(k)

Unfortunately, this code invokes f(k) twice. How would you find k and f(k) at once ?

Answer 1

My first try would be:

(1 to 10).view map {k => (k, f(k))} find {_._2.isDefined}

The use of view avoids creating intermediate map. Or even better with pattern matching and partial function:

(1 to 10).view map {k => (k, f(k))} collectFirst {case (k, Some(v)) => (k, v)}

This returns Option[(Int, java.lang.String)] (None if no element satisfying f is found).

You might also experiment with .zipWithIndex.