[R] generalized matrix product ?

[Huntsinger, Reid]

Say you have a function FUN of two vector arguments which operates
"columnwise on arrays". E.g., if FUN(v,w) is to be the inner product, then
instead of v%*%t(w) write something like colSums(v*w). Now you can do
something like

vectorOuterProd <- function(A,B,FUN) {
  da <- dim(A)[-1] 
  na <- prod(da)
  db <- dim(B)[-1]
  nb <- prod(db)
  
  result <- matrix(nrow=na,ncol=nb)
  dim(B) <- c(dim(B)[1],nb)
  for (j in 1:nb) {
    result[,j] <- FUN(A,B[,j])
  }
  dim(result) <- c(da,db)
  result
}

which loops over the columns of B rather than replicate A and B as in
outer() to save space. 

Reid Huntsinger
-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of George_Heine at blm.gov
Sent: Friday, April 29, 2005 2:24 PM
To: r-help at stat.math.ethz.ch
Subject: [R] generalized matrix product ?






Is there available in R a generalized inner product or matrix product,
similar to 'outer(x,y, fun)', where one can specifiy an arbitrary function
in place of ordinary multiplication?

Here's my application.  I frequently analyze user questionnaires from our
HR/training department.  These have questions of the form
     "please rate your skill in task X",
 and other questions of the form
     "Have you taken course Y?"  (or "How many years since you have taken
course Y?")

I look at rank correlation between the (suitably ordered) vectors of
responses to a question in the first group and a question in the second
group.  (The two vectors have the same length, but I want to replace the
standard inner product with a different operation; in this case, rank
correlation)  Repeat the process across all possible pairs of questions.

Is there a way to accomplish this without nested 'for' statements?

Hope this is clear - thanks!
<>=<>=<>=<>=<>=<>=<>=<>=<>=<>=<>
George Heine, PhD
Mathematical Analyst
National IRM Center
U.S. Bureau of Land Management
voice   (303) 236-0099
fax       (303) 236-1974
cell      (303) 905-5382
pager   gheine at my2way.com
<>=<>=<>=<>=<>=<>=<>=<>=<>=<>=<>t

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