-----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