generalized matrix product ?
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