Acting on inner and outer loops for multidimensional array in idiomatic scala

Question

I have this nested loop:

for ( y <- 0 to 5) {
    for ( x <- 0 to 5) {
        print(x, y)
    }
    println()
}

Is there a cleaner way of expressing this in scala -- bearing in mind I want to do something once for every outer loop iteration, as well as the internal?

The following is the closest I've got:

for {
    y <- 0 to 5
    x <- 0 to 5
} {
    print (x, y) + " "
    if(x == 5) println()
}

V-Lamp · Accepted Answer · 2018-01-09 11:51:00Z

1

  for {
    y <- 0 to 5
    x <- 0 to 5
    _ = if (x ==5) println()
  } print(x, y)

Seems like the most concise way to me.

answered Jan 9, 2018 at 11:51

V-Lamp

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2 Comments

Tim Barrass Over a year ago

That's interesting -- it doesn't do the final println that the original does. I don't understand this structure, will have to look it up :)

Tim Barrass Over a year ago

ah, you're using _ to throw away the return of the guard?

F. Lins · Accepted Answer · 2018-01-09 17:09:31Z

1

I don't think for comprehensions are a good option here, why not just use foreach? like this:

(0 to 5).foreach{ y =>
  (0 to 5).foreach{ x =>
    print (x, y) + " "
  }
  println()
}

edited Jan 9, 2018 at 17:09

answered Jan 9, 2018 at 15:23

F. Lins

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3 Comments

Tim Barrass Over a year ago

Moving the println after the inner loop means it replicates the original behaviour. Do you have a reason in mind for why for comprehensions aren't a good option here?

F. Lins Over a year ago

I edited the code according to your comment. For-comprehensions are in general used when you want to compile multiple results in one and not really helpful if you want to process partials. For example, if you have three Options and you use a for comprehension to merge them into one object, it's impossible to know which one is a None, same thing with tries.

Tim Barrass Over a year ago

Reading around it appears that for-comprehensions are actually translated into foreach (or map, flatmap etc), meaning the for-comprehension is just syntactic sugar. See for example: docs.scala-lang.org/tutorials/FAQ/yield.html

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