[R] Extracting from a matrix w/o for-loop

From: Camarda, Carlo Giovanni <Camarda_at_demogr.mpg.de>
Date: Sat 29 Jul 2006 - 02:40:14 EST


Dear R-users,

likely there is a simple solution for this problem, but I currently cannot see it.

I basically would like to get from a matrix values in particular positions which are the rows of another matrix, without using a for-loop.

In other words: is there any way to avoid the for-loop in the following simple example:

M1 <- matrix(1:20, ncol=2)
M2 <- rbind(c(1,1), c(2,1), c(3,2), c(5,2), c(8,1)) v <- numeric(nrow(M2))
for(i in 1:length(v)){

    v[i] <- M1[M2[i,1], M2[i,2]]
}

Any suggestion would be welcome,

Ciao,
Carlo Giovanni Camarda



Camarda Carlo Giovanni
PhD-Student
Max Planck Institute for Demographic Research Konrad-Zuse-Strasse 1
18057 Rostock, Germany
Tel: +49 (0)381 2081 172
Fax: +49 (0)381 2081 472
camarda@demogr.mpg.de


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