[R] updating n within for(i in 1:n) loop

[Timothy H. Keitt]

The problem is that the '1:n' in 'for(i in 1:n)' is only evaluated once
at the beginning of the loop, so altering 'n' later does not change the
loop behavior. Try something like:

i <- 0
repeat {
	i <- i + 1
	cat(i, '\n')
	if (i > 9) break
}

T.

On Mon, 2002-08-26 at 14:50, Huntsinger, Reid wrote:
> I think a while or repeat is what you want. I believe the 1:n in the for
> loop is evaluated only once, at the beginning, but I could be wrong.
> 
> Reid Huntsinger
> 
> -----Original Message-----
> From: Prasad, Rajiv [mailto:Rajiv.Prasad at pnl.gov]
> Sent: Monday, August 26, 2002 1:55 PM
> To: R-Help (E-mail)
> Subject: [R] updating n within for(i in 1:n) loop
> 
> 
> Hi folks:
> 
> I think I'm having problems with figuring this one out:
> 
> test1 <- function()
> {
>   n <- 2
> 
>   for(i in 1:n)
>   {
>     cat(paste("i =", i, "\n")); flush.console()
>     n <- 5  # version 1
>     #n <<- 5  # version 2
>     #assign("n", 5, envir = environment(test1))  # version 3
>   }
> }
> 
> I need the for(.) loop to run (say) n=5 times within the function, but I do
> not know that before the loop begins.  In other words, n is to be updated
> during computations within the for(.) loop.  This code prints "i = 1" and "i
> = 2" only.  If I modify test1(.) to use version 2 or version 3 of the
> assignment, there is no change to the output, and I end up with an "n" in
> the parent environment with value 5.  So the problem is to assign 5 to n in
> the calling environment of the for(.) loop??  (I'm sure my terminology is
> quite mixed up here -- please feel free to comment.)
> 
> How do I do this?
> 
> Thanks in advance.
> 
> > version
>          _              
> platform i386-pc-mingw32
> arch     i386           
> os       mingw32        
> system   i386, mingw32  
> status                  
> major    1              
> minor    5.1            
> year     2002           
> month    06             
> day      17             
> language R              
> 
> 
> Rajiv
> --------
> Rajiv Prasad
> Postdoctoral Research Associate, Hydrology Group
> Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-33
> Richland, WA 99352
> Voice: (509) 375-2096  Fax: (509) 372-6089  Email: rajiv.prasad at pnl.gov
> 
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