updating n within for(i in 1:n) loop

Mon, Aug 26, 2002 2:09 PM

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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updating n within for(i in 1:n) loop

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