R help - Apr 2012 - problem with break command

Hello R-users,

I am having a problem with the 'break' command in R. I am wondering if
anyone can help me out with this. My program is similar to the following.

a=rep(NA,5)
a[1]=0
for(i in 2:5)
{
    a[i]=a[i-1]+runif(1,0,3)
    if(a[i]>5)
    {
        i=2
        break
    }
}

What exactly I am trying to do is find the sequence 'a' where the
individual values of 'a' would not be larger than 5. In any sequence, if
it
becomes larger than 5, it would set the counter to be 2 and regenerate from
i=2. But I guess I have not put the break command in the right place, so
even though the 'if' condition becomes true and it sets i=2, it does not
regenerate the values of 'a' since the beginning. Any help is really
appreciated.

Thanks in advance.

Cassie

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On 26-04-2012, at 21:30, cassie jones wrote:
> Hello R-users,
> 
> I am having a problem with the 'break' command in R. I am wondering
if
> anyone can help me out with this. My program is similar to the following.
> 
> a=rep(NA,5)
> a[1]=0
> for(i in 2:5)
> {
>    a[i]=a[i-1]+runif(1,0,3)
>    if(a[i]>5)
>    {
>        i=2
>        break
>    }
> }
> 
> What exactly I am trying to do is find the sequence 'a' where the
> individual values of 'a' would not be larger than 5. In any
sequence, if it
> becomes larger than 5, it would set the counter to be 2 and regenerate from
> i=2. But I guess I have not put the break command in the right place, so
> even though the 'if' condition becomes true and it sets i=2, it
does not
> regenerate the values of 'a' since the beginning. Any help is
really
> appreciated.

break will exit the for loop. You cannot achieve what you desire with break.

You need a while loop for this.

i <- 2
while( i <= 5 )
# for(i in 2:5)
{
   a[i] <- a[i-1]+runif(1,0,3)
   if(a[i]>5) i <- 2 else i <- i+1
}

And hope that the while loop will eventually terminate.

Berend

On Thu, Apr 26, 2012 at 02:30:09PM -0500, cassie jones
wrote:
> Hello R-users,
> 
> I am having a problem with the 'break' command in R. I am wondering
if
> anyone can help me out with this. My program is similar to the following.
> 
> a=rep(NA,5)
> a[1]=0
> for(i in 2:5)
> {
>     a[i]=a[i-1]+runif(1,0,3)
>     if(a[i]>5)
>     {
>         i=2
>         break
>     }
> }
Hi.

Berend sent you a solution.

Perhaps, one thing concerning the for loops in R should be
clarified. The variable specified as the loop variable is
not the true loop variable, which controls the loop, since
one can have a loop for (i in c(1, 1, 1, 1, 1)). The true
control variable is hidden and cannot be changed. So the
for loop

  for (i in 1:3) {
      for (i in 1:4) {
          cat("*")
      }
      cat("\n")
  }

works correctly although the visible loop variables are the
same.

Petr Savicky.