[R] be careful: using attach in R functions
Roger D. Peng
rpeng at jhsph.edu
Tue Feb 24 22:20:42 CET 2004
Using attach() in this context may not be wise. I tend to only use
attach() when working interactively. It might be better to use with()
in this situation, such as
f <- function() {
theta <- list(one=2.0, two=0.3, three=0.4)
x <- with(theta, c(one, two, three))
sample(x, 1)
}
-roger
li dongfeng wrote:
> 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()
> ##############################
>
>
> ããããããããLi Dongfeng
> ããããããããldf-nospacm at math.pku.edu.cn
> ãããããããããã2004-02-24
>
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