Thanks, Henrique! Your approach definitely works and gives the result that I need, but the calculations takes quite a while. As this problem itself is part of loop (Markov Chain), I am still looking for faster and truely vectorized solutions, maybe after a re-organisation of the data matrices?
I'd be grateful for any further suggestions! Henrique Dallazuanna wrote: > > Perhaps: > n.obs = 800 > n.rowsperobs = 300 > n.param = 23 > > Designmat = matrix(rnorm(n.obs*n.rowsperobs*n.param),ncol=n.param) > > Betamat = matrix(rnorm(n.obs*n.param),nrow=n.param) > > Design.spl <- split(as.data.frame(Designmat), rep(1:n.obs, > each=n.rowsperobs)) > res <- sapply(1:ncol(Betamat), > function(x)as.matrix(Design.spl[[x]])%*%Betamat[,x]) > > > > On 20/01/2008, Ralph79 <[EMAIL PROTECTED]> wrote: >> >> Dear R-users, >> >> I am working on a problem that I am currently not able to solve >> efficiently. >> It is about multiplying one column of a matrix with only a certain number >> of >> rows of another matrix. >> >> Let me illustrate my problem with an example: >> >> n.obs = 800 >> n.rowsperobs = 300 >> n.param = 23 >> >> Designmat = matrix(rnorm(n.obs*n.rowsperobs*n.param),ncol=n.param) >> >> Betamat = matrix(rnorm(n.obs*n.param),nrow=n.param) >> >> In this example, "Designmat" consists of 800*300 rows, meaning that 300 >> rows >> belong to one of the 800 observations. >> >> Each observation has also one parameter vector, which is one column in >> the >> "Betamat"-matrix (i.e. Betamat contains the n.obs parameter vectors). >> >> My goal is to multiply the parameter vector of each observation (i.e. the >> respective column in Betamat) with ONLY THOSE ROWS IN DESIGNMAT that >> belong >> to this observation. >> Applied to the example above: The first column in Betamat has to be >> multiplied with the first 300 rows in Designmat, the second column in >> Betamat has to be multiplied with rows 301 to 600 in Betamat and so on. >> Hence, the result of this operation should be a vector of length 240000. >> >> I can think of solutions implying several loops and/or lapplys, but I >> guess >> that there might be a much easyer and above all faster solution. >> >> Thank you very much for your help in advance. >> >> -- >> View this message in context: >> http://www.nabble.com/Efficient-way-for-multiplying-vectors-with-a-only-certain-number-of-rows-in-a-matrix-tp14988427p14988427.html >> Sent from the R help mailing list archive at Nabble.com. >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > > -- > Henrique Dallazuanna > Curitiba-Paraná-Brasil > 25° 25' 40" S 49° 16' 22" O > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > > -- View this message in context: http://www.nabble.com/Efficient-way-for-multiplying-vectors-with-a-only-certain-number-of-rows-in-a-matrix-tp14988427p14995032.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
