CODEWITHSUNDEEP
scalafor-loop
cozyss
cozyss

Reputation: 1388

How to execute only the outer for loop in scala?

In Scala, what if I have a nested for loop, and I want to execute different things on each one.

for (int i = 0; i<5; i++) {
   System.out.println(i);       //do something for just i
   for(int j = 0; j<5; j++) {
      System.out.println(i+j);  //do something for both i and j
   }
}

But the scala code:

for {i<-0  to 5 
     j<- 0 to 5} yield { print(i); print(i+j)}

gives the output:

    0
(0,0)
0
(0,1)
0
(0,2)
0
(0,3)
0
(0,4)
0
(0,5)

but I want it to be:

0
(0,0)
(0,1)
(0,2)
(0,3)
(0,4)
(0,5)

Is there a way to only print i for each i, and i+j for each i and j in ONE for loop?

Upvotes: 0

Views: 94

Answers (3)

jwvh
jwvh

Reputation: 51271

The compiler rewrites for comprehensions into their constituent map(), flatMap(), foreach(), and withFilter() parts. That's why some of the normal rules of Scala syntax don't apply inside sequence comprehension expressions. They get mangled in the rewriting process.

There are a few tricks to get around the problem.

for {
  i <- 0 to 5
  _ = println(i)
  j <- 0 to 5
} yield // do stuff with i and j

It really depends on what you need to do with the i value. It could be that a for comprehension is not the best tool for the job.

Upvotes: 3

Ramesh Maharjan
Ramesh Maharjan

Reputation: 41957

Alternative way of doing the same would be to use map function as following 

val loop = 0 to 5
loop.map(i => {
  println(i) // do your stuffs as you did for i
  loop.map(j => {
    println(i, j) //do your stuffs as you did for i, j 
  })
})

Upvotes: 1

Sohum Sachdev
Sohum Sachdev

Reputation: 1397

I think this will do the trick:

(0 to 5).zip(0 to 5).foreach{case (i, j) => 
    //do stuff to i an dj
}

Upvotes: 1

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