Large loops in R
Without a reproducible example it's hard to tell for certain, but what about simply (assuming nrows2 is actually columns): sum((mat1/d1 - mat2/d2)^2) R is smart enough to understand elementwise manipulation of a matrix: you shouldn't need a loop at all. Sarah On Tue, Dec 4, 2012 at 2:27 PM, Charles Novaes de Santana
<charles.santana at gmail.com> wrote:
Dear Michael,
Thank you for your answer.
I have 2 matrices. Each position of the matrices is a weight. And I
need to calculate the following sum of differences:
Considering:
mat1 and mat2 - two matrices (each of them 48000 x 48000).
d1 and d2 - two constant values.
sum<-0;
for(i in 1:nrows1){
for(j in 1:nrows2){
sum<-sum+ ( ( (mat1(i,j)/d1) -
(mat2(i,j)/d2) )^2 )
}
}
}
I was wondering if there is a better way to do this sum.
Thank you for your attention!
Best,
Charles
On Tue, Dec 4, 2012 at 7:54 PM, R. Michael Weylandt
<michael.weylandt at gmail.com> <michael.weylandt at gmail.com> wrote:
On Dec 4, 2012, at 6:47 PM, Charles Novaes de Santana <charles.santana at gmail.com> wrote:
Dear all, I need to access data from a large matrix (48000 x 48000) and to do it I am trying to run two loops using "for" command. Surely it is been a very slow job. I heard that "for" is not the best option to perform large loops in R, but I don't really know what would be the best (fast) option. sapply? vapply? Could anyone help me with this issue, please?
What exactly are you trying to do? It's likely doable with a few vectorized operations. Michael
-- Sarah Goslee http://www.functionaldiversity.org