What's wrong with
num <- rep(0,10)
done <- FALSE
i <- 2
while(!done){
num[i] <- num[i-1] + 5
if(num[i] > 20) done <- TRUE
i <- i + 1
}
num <- num[1:(i-1)]
You can delete the unused tail when you finish. Iteratively
reassigning to a vector of undefined length is possible too, but that
is much slower:
> x <- numeric()
> system.time(for(i in 1:100000){ x[i] <- i})
user system elapsed
29.641 27.509 57.163
> y <- numeric(100000)
> system.time(for(i in 1:100000){ y[i] <- i})
user system elapsed
0.537 0.000 0.532
>
albyn
On Tue, Apr 10, 2012 at 11:53:08AM -0400, Steve Lavrenz wrote:
> Albyn,
>
> Thanks for your help. This however, still assumes that I have to define an
> array of length 10. Is there a way that I can construct this so that my
> array is exactly as long as the number of spots I need to reach my threshold
> value?
>
> Thanks,
>
> -Steve
>
> -----Original Message-----
> From: Albyn Jones [mailto:jo...@reed.edu]
> Sent: Tuesday, April 10, 2012 11:46 AM
> To: Steve Lavrenz
> Cc: r-help@r-project.org
> Subject: Re: [R] Creating a loop with an indefinite end term
>
> Here are a couple of constructions that work.
>
> albyn
> ===========================================
>
> num <- rep(0,10)
> for (i in 2:10) {
> num[i] <- num[i-1] + 5
> if(num[i] > 20) break
> }
> > num
> [1] 0 5 10 15 20 25 0 0 0 0
>
> or
>
> num <- rep(0,10)
> done <- FALSE
> i <- 2
> while(!done){
> num[i] <- num[i-1] + 5
> if(num[i] > 20) done <- TRUE
> i <- i + 1
> }
> > num
> [1] 0 5 10 15 20 25 0 0 0 0
>
>
> On Tue, Apr 10, 2012 at 10:48:34AM -0400, Steve Lavrenz wrote:
> > Everyone,
> >
> > I'm very new to R, especially when it comes to loops and functions, so
> > please bear with me if this is an elementary question. I cannot seem
> > to figure out how to construct a loop which runs a function until a
> > certain value is computed. For example, say I have the following:
> >
> > num = numeric (10)
> > num [1] = 0
> > for (i in 2:10) {
> > num [i] = num [i-1] + 5
> > }
> >
> > This adds 5 to the preceding spot of a vector of length 10 to get the
> > value in the current spot. However, say I don't just want to run this
> > for 10 spots; rather I want to run it until a certain value (say, 100) is
> computed.
> > How I construct my loop to do this?
> >
> > Thanks!
> >
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
> --
> Albyn Jones
> Reed College
> jo...@reed.edu
>
>
>
--
Albyn Jones
Reed College
jo...@reed.edu
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