Re: [R] Efficient way for multiplying vectors with a only certain number of rows in a matrix

From: Henrique Dallazuanna <wwwhsd_at_gmail.com>
Date: Sun, 20 Jan 2008 23:39:05 -0200

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 <ralph.statistics_at_gmx.net> 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_at_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_at_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.
Received on Mon 21 Jan 2008 - 01:45:17 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Mon 21 Jan 2008 - 11:30:07 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.

list of date sections of archive