Avoid mutable variable in for loop

Question

I have some code like below. But I wish to avoid this mutable variable flag.

How can I achieve this?

  def map(s: Set, f: Int => Int): Set = (x: Int) =>  {
    var flag : Boolean = false
    for(i <- -bound to bound) {
      if(s(i) && f(i) == x){
        flag = true
      }
    }
    flag
  }

I don't know scala at all, but I image you could use a while loop instead of a for loop. while(!s(i) || f(i)!=x) — alanmanderson
– alanmanderson, Commented Sep 27, 2012 at 7:18
Yes this is a coursera question, and it should be solved with a simple one-liner, not a loop (not that that matters to the question as such). — Frank
– Frank, Commented Sep 27, 2012 at 8:59

venechka · Accepted Answer · 2012-09-27 07:19:51Z

5

I think you need this simple test:

(-bound to bound) exists {i => s(i) && f(i) == x}

answered Sep 27, 2012 at 7:19

venechka

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Comments

dhg · Accepted Answer · 2012-09-27 07:19:45Z

3

Use the exists collection method. The exists method returns true if the specified condition is true for at least one element in the collection, and false otherwise.

def map(s: Set[Int], f: Int => Int): (Int => Boolean) =
  (x: Int) => {
    (-bound to bound).exists(i => s(i) && f(i) == x)
  }

answered Sep 27, 2012 at 7:19

dhg

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1 Comment

Rahel Lüthy Over a year ago

While I really don't want to support giving away solutions, I would at least want to give a pointer towards a better one: The hint about using exists is good. If exists is implemented as required in the assignment, it calls foreach, which already loops from -bound to bound. TL;DR: Aim at a ~25 char solution which does not require extra iteration but does the trick in the function it passes to exists.

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