[R] be careful: using attach in R functions
Liaw, Andy
andy_liaw at merck.com
Tue Feb 24 20:13:40 CET 2004
You can write your code more defensively. There are a few ways to do that:
1. Right after the attach(object), do on.exit(detach(object)).
2. If you know the function will be call repeatedly, it might be a good idea
to check whether the object has been attached. This way you only need to
attach once. I can think of a couple of way to do that. The simplest is
probably to check and see if the object name appear in the search list.
Andy
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of li dongfeng
> Sent: Monday, February 23, 2004 1:00 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] be careful: using attach in R functions
>
>
> Hi there,
>
> I have just found that the ``attach'' function
> can get you into trouble when called many times.
> For example, you have a simulation routine called ``f()'',
> in which you used ``attach'' and no corresponding ``detach''.
> Then you call this function many times. You will find that
> the system performance get slower and slower,
> because you are making the R search path longer and longer.
> So be careful when you use attach in a function!
>
> Below is a demonstration of this performance loss,
> you will see a linear growth in CPU time usage.
> Adding a ``detach()'' call at the end of ``f''
> will get rid of this problem.
>
> ###############################
> f <- function(){
> theta <- list(one=2.0, two=0.3, three=0.4)
> attach(theta)
> x <- c(one, two, three)
> sample(x, 1)
> }
>
> test <- function(n=400){
> timeu <- numeric(n)
> for(i in seq(n)){
> timeu[i] <-
> system.time({
> resi <- f()
> })[3]
> }
> plot(timeu)
> }
> test()
> ##############################
>
>
> Li Dongfeng
> ldf-nospacm at math.pku.edu.cn
> 2004-02-24
>
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