[R] labeled break statements in R?

[Gabor Grothendieck]

Gabor Grothendieck <ggrothendieck <at> myway.com> writes:
> Roger Levy <rog <at> stanford.edu> writes:
> : Are there labeled break statements in R?  i.e., something along the
> : lines of
> : 
> : TOPLOOP: for(i in 1:m) {
> :   for(j in 1:n) {
> :     ...
> :     if(condition) {
> :        break TOPLOOP
> :     }
> :   }
> : }
> 
> Assuming that your labelled break is supposed to break out of
> both loops, unlike an ordinary break that just breaks out of
> the inner loop, this is how it would be done:
> 
> a <- matrix(0, nr=3, nc=3)
> local({
> 	for(i in 1:3) 
> 		for(j in 1:3)
> 			if (i+j>4) return() else a[i,j] <<- i+j
> })
> a
> 
> Be aware that assigning variables within the local will assign
> local copies unless you use <<-, assign(..., ..., parent.frame())
> or eval.parent(...).

An improvement over the above is to use evalq as this does not set
up a local environment, thereby avoiding the problems cited in
the last sentence:

a <- matrix(0, nr=3, nc=3)
evalq({
     for(i in 1:3)
          for(j in 1:3)
               if (i+j>4) return() else a[i,j] <- i+j
})
a

Note that we were able to replace the <<- with <-.