Julia - Continue outer loop

Question

I am currently porting an algorithm from Java to Julia and now I have come across a part where I have to continue an outer loop from an inner loop when some condition is met:

 loopC: for(int x : Y){
            for(int i: I){
                if(some_condition(i)){
                    continue loopC;
                }                   
            }
        }

I have found some issues on GitHub on this topic but there seems to be only a discussion about it and no solution yet. Does anybody know a way how to accomplish this in Julia?

Eph

Answer 1

As in some other languages julia uses break for this:

for i in 1:4
    for j in 1:4
        if j == 2
            break
        end
    end
end

breaks out of the inner loop whenever j is 2

However, if you ever need to exit the outer loop you can use @goto and @label like so

for i in 1:4
    for j in 1:4
        if (j-i) == 2
            @goto label1
        end 

        if j == 2 
            @goto label2
        end 
        do stuff
    end 
    @label label2
end 
@label label1

Straight from the julia docs http://docs.julialang.org/en/release-0.5/manual/control-flow/

It is sometimes convenient to terminate the repetition of a while before the test condition is falsified or stop iterating in a for loop before the end of the iterable object is reached. This can be accomplished with the break keyword

Glebe

This works! But the link no longer works, and this method of doing things is no longer in the docs. – Palmitate

Answer 2

As mentioned by @isebarn, break can be used to exit the inner loop:

for i in 1:3
    for j in 1:3
        if j == 2
            break # continues with next i
        end  
        @show (i,j)  
    end # next j  
end # next i   
(i, j) = (1, 1)
(i, j) = (2, 1)
(i, j) = (3, 1)

However, some caution is required because the behaviour of break depends on how the nested loops are specified:

for i in 1:3, j in 1:3
    if j == 2
        break # exits both loops
    end  
    @show (i,j)  
end # next i,j   
(i, j) = (1, 1)  

See https://en.wikibooks.org/wiki/Introducing_Julia/Controlling_the_flow#Nested_loops

It is also possible, albeit cumbersome, to return from a nested function that contains the inner loop:

for i in 1:3  
    (i -> for j in 1:3  
         if j == 2  
             return  
         end  
         @show (i,j)  
    end)(i)
end  
(i, j) = (1, 1)
(i, j) = (2, 1)
(i, j) = (3, 1)

Nemato

Answer 3

This can be achieved using flags:

for i in 1:3  
    flag = false
    for j in 1:3  
         if j == 2  # some condition
             flag = true
             break
         end  
    end
    if flag
        continue
    end
    #...
end  

Loadstone