setMethod("c") [was: setMethod("Summary")]
It's all very well to go on about efficiency, but the purpose of
statistical computing is insight into data, not saving CPU cycles (to
paraphrase Dick Hamming).
S3 methods do some things fine; other tasks need more flexibility. One
should ask what's important in a particular application and try to find
tools that match the needs well.
Now, the c() function. This has been discussed in various forms (and
languages) for some time. As I remember and as far as I know, the only
really general way to ensure dispatch on _any_ applicable argument is to
turn the computation into a pair-wise one and define the methods (NOT S3
methods) for the two arguments of the pairwise function.
I won't try to reproduce the details off the top of my head (if I locate
a reference I'll pass it on), but very roughly the idea is to say
something like
cWithMethods <- function(x, ...) {
if(nargs()<3)
cPair(x,...)
else
cPair(x, cWithMethods(...))
}
and then write methods for cPair().
John
Robin Hankin wrote:
Hello everybody.
I didn't see Franklin's first message; sorry.
Bearing in mind Professor Ripley's comments
on the efficiency of S4 vs S3, I'm beginning to think I
should just stick with S3 methods for my brob objects. After
all, S3 was perfectly adequate for the onion package.
Notwithstanding that, here's my next problem. I want to define a
brob method for "c". Using the example in package "arules" as a
template (I couldn't see one in Matrix), I have
setClass("brob",
representation = representation
(x="numeric",positive="logical"),
prototype = list(x=numeric(),positive=logical())
)
"brob" <- function(x,positive){
if(missing(positive)){
positive <- rep(TRUE,length(x))
}
if(length(positive)==1){
positive <- rep(positive,length(x))
}
new("brob",x=x,positive=positive)
}
setGeneric("getX",function(x){standardGeneric("getX")})
setGeneric("getP",function(x){standardGeneric("getP")})
setMethod("getX","brob",function(x){x at x})
setMethod("getP","brob",function(x){x at positive})
setMethod("c",signature(x="brob"),
function(x, ..., recursive=FALSE){
xx <- x at x
xpos <- x at positive
z <- list(...)
return(
brob(
c(xx,do.call("c",lapply(z,getX))),
c(xpos,do.call("c",lapply(z,getP)))
)
)
}
)
Now, this works for something like
> x <- new("brob",x=pi,positive=T)
> c(x,x)
but c(1,x) isn't dispatched to my function. How to deal cleanly with this case? Perhaps if any argument to c() is a brob object, I would like to coerce them all to brobs. Is this possible? -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743
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