[R] Loops that last for ever...

From: Constantine Tsardounis <costas.magnuse_at_gmail.com>
Date: Tue 31 Jan 2006 - 04:41:11 EST


Hello, good morning or evening!...

After studying some of the examples at S-poetry Document, I tried to implement some of the concepts in my R script, that intensively uses looping constructs. However I did not manage any improvement. My main problem is that I have a list of a lot of data e.g.:
> xs

[[1]]
[1]........................[1000]
[[2]]
[1]........................[840]

...
[[50]]
[1]........................[945]


Having a script with loops inside loops (for example in a Monte-Carlo simulation) takes a lot of minutes before it is completed. Is there another easier way to perform functions for each of the [[i]] ? Using probably apply? or constructing a specific function? or using the so-called "vectorising" tricks?

One example could be the following, that calculates the sums 1:5, 2:6, 3:7,..., for each of xs[[i]] :

xs <- lapply(1:500, function(x) rnorm(1000)) totalsum <- list()
sums <- list()
first <- list()

for(i in 1:length(xs)) {
totalsum[i] <- sum(xs[[i]])

	for(j in 1:length(xs[[i]])) {
		if(j == 1) {
			sums[[i]] <- list()
			}
		if(j >= 5) {
			sums[[i]][j] <- sum(xs[[i]][(j-4):j])
			}
		}

}

Of course the functions I actually call are more complicated, increasing the total time of calculations to a lot of minutes,...

<< 1 >>. How could I optimize (or better eliminate?...) the above loop? Any other suggestions for my scripting habits?

Another problem that I am facing is that calculating a lot of lists (>50), that contain results of various econometric tests of all the variables, in the form of

   example.list[[i]] <- expression

demands more than 50 lines at the beginning of the script that "initiate" the lists (e.g.
example.list.1 <- list()
example.list.2 <- list()
...

example.list.50 <- list()

<< 2 >>. Is there a way to avoid that?

Thank you very very much in advance,

Constantine Tsardounis



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jan 31 04:52:08 2006

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:42:15 EST