Hello,
Package 'compiler' is good at optimizing for loops. Try the following.
#install.packages('compiler')
library(compiler)
f1.c <- cmpfun(f1)
N <- 1e6
x <- rnorm(N)
system.time(f1(x, 10))
user system elapsed
6.77 0.06 6.83
system.time(f1.c(x, 10))
user system elapsed
2.57 0.00 2.57
Hope this helps,
Rui Barradas
Em 27-11-2012 21:43, 47 escreveu:
I'd like to write a function that has a vector and a (pos.) number as inputs
and returns what is on the picture below (arithmetic means of (k)
consecutive elements of a given vector). The problem is it works too slow
for long vectors and i know it can be done without "for" loop. However, i've
got no idea how. Can anyone help me with that?
f1 <- function(v,k) {
n <- length(v)
z <- (n-k+1)
for (i in k:n) {
v[i-k+1] <- sum(v[(i-k+1):i])
}
v <- v[1:(n-k+1)]
v <- v/k
return (v)
}
<http://r.789695.n4.nabble.com/file/n4651030/Untitled.png>
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