[R] generalized matrix product ?

[Gabor Grothendieck]

On 4/29/05, George_Heine at blm.gov <George_Heine at blm.gov> wrote:
> 
> 
> 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?

Try this:

inner <- function(a,b,f, ...) {
		f <- match.fun(f)
		apply(b,2,function(x)apply(a,1,function(y)f(x,y, ...)))
}

data(iris); irish <- head(iris)[,-5]  # test data
res <- inner(t(irish), irish, cor, method = "spearman")  # test

res2 <- cor(irish, method = "spearman") # should give same result
identical(res, res2) # TRUE