R help - Sep 2014 - Issue with a function

Hi,

I'm trying to use a function to multiply a matrix (newX) with a simple list
(beta).
I know that I can simply use matrix multiplication i.e. newX %*%as.matrix(beta)
and this works fine. However, the matrix multiplication gives me the sum of each
row. What I really need are the new values of all the columns in newX if they
were multiplied by beta (so the first column of newX should be multiplied by the
first value in beta, second column by the second value etc..)

This is the function I'm trying to use:

Terms <-NULL
count <- 0

for (i in 1: ncol(newX)){
  for (j in 1: length(beta)){
    Terms <- cbind (Terms,(newX[,i]*beta[j]))
  }
}

I don't get an error message, however the function runs for a long time
(about an hour) without resolving and I end up stopping it.



Now, if I multiply every individual column by each value of beta, the
calculation works (code is below):
newX[,1]*beta[1]
newX[,2]*beta[2]

but since newX has 520 columns and beta has 520 values, I'd rather use a
shortcut!!


I can't figure out why the above function doesn't work. I've used it
to multiply two matrices and it works just fine.
Any insight would be appreciated.

Yara

library(Matrix)
result <- newX %*% Diagonal( unlist(beta) )

Is beta really a list, or is it a vector? The str function can help with this...
in most cases it is a numeric mode vector and the unlist is not needed.
---------------------------------------------------------------------------
Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...1k
--------------------------------------------------------------------------- 
Sent from my phone. Please excuse my brevity.

On September 29, 2014 5:03:30 PM PDT, Yara Abu Awad <yara_abuawad at
yahoo.com> wrote:
>Hi,
>
>I'm trying to use a function to multiply a matrix (newX) with a simple
>list (beta).
>I know that I can simply use matrix multiplication i.e. newX
>%*%as.matrix(beta)
>and this works fine. However, the matrix multiplication gives me the
>sum of each row. What I really need are the new values of all the
>columns in newX if they were multiplied by beta (so the first column of
>newX should be multiplied by the first value in beta, second column by
>the second value etc..)
>
>This is the function I'm trying to use:
>
>Terms <-NULL
>count <- 0
>
>for (i in 1: ncol(newX)){
>  for (j in 1: length(beta)){
>    Terms <- cbind (Terms,(newX[,i]*beta[j]))
>  }
>}
>
>I don't get an error message, however the function runs for a long time
>(about an hour) without resolving and I end up stopping it.
>
>
>
>Now, if I multiply every individual column by each value of beta, the
>calculation works (code is below):
>newX[,1]*beta[1]
>newX[,2]*beta[2]
>
>but since newX has 520 columns and beta has 520 values, I'd rather use
>a shortcut!!
>
>
>I can't figure out why the above function doesn't work. I've
used it to
>multiply two matrices and it works just fine.
>Any insight would be appreciated.
>
>Yara
>
>______________________________________________
>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.