R help - Nov 2007 - interaction of shingles and tapply()

I'm interested in a version of tapply() that operates with shingles 
instead of factors.  For instance:

x <- c(1,1,2,2,3,3)
y <- c(1,1,1,0,0,0)

s <- shingle(x,intervals=cbind(c(0.5,1.5),c(2.5,3.5)))


# the following function should exist!
tapply.shingle(x,s,mean)  # returns the vector c(0.75,0.25)


I've written such a function as follows:


tapply.shingle <- function(x,s,fn,...) {
   result <- c()
   for(l in levels(s)) {
     x1 <- x[s > l[1] & s < l[2]]
     result <- c(result, fn(x1,...))
   }
   result
}


However, I'm not thrilled with the for() loop, and I don't see any way 
to generalize this function to handle lists of shingles instead of 
individual shingles, except to use recursion.  Does anyone have any 
suggestions or thoughts?

Many thanks,

Roger

One way to get rid of the 'for' loop:

tapply.shingle <- function(x, s, fn, ...){
    unlist(lapply(levels(s), function(.val) mean(x[s > .val[1] & s <
.val[2]], ...))
}


On Nov 27, 2007 8:56 PM, Roger Levy <rlevy at ucsd.edu>
wrote:
> I'm interested in a version of tapply() that operates with shingles
> instead of factors.  For instance:
>
> x <- c(1,1,2,2,3,3)
> y <- c(1,1,1,0,0,0)
>
> s <- shingle(x,intervals=cbind(c(0.5,1.5),c(2.5,3.5)))
>
>
> # the following function should exist!
> tapply.shingle(x,s,mean)  # returns the vector c(0.75,0.25)
>
>
> I've written such a function as follows:
>
>
> tapply.shingle <- function(x,s,fn,...) {
>   result <- c()
>   for(l in levels(s)) {
>     x1 <- x[s > l[1] & s < l[2]]
>     result <- c(result, fn(x1,...))
>   }
>   result
> }
>
>
> However, I'm not thrilled with the for() loop, and I don't see any
way
> to generalize this function to handle lists of shingles instead of
> individual shingles, except to use recursion.  Does anyone have any
> suggestions or thoughts?
>
> Many thanks,
>
> Roger
>
> ______________________________________________
> 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?