Message-ID: <4B179B23.3030903@cam.ac.uk>
Date: 2009-12-03T11:04:03Z
From: robin hankin
Subject: S4 and head() problems
Hi
I am having difficulty defining an S4 method for head() and tail().
I can't quite provide minimal self-contained code
because the problem appears to require the whole corpus
of my package; and there also appears to be a difference
between sourcing the lines directly, and having them
installed in a package.
The lines in question (I think) are:
setClass("mdm",
representation = representation(
xold = "matrix",
types = "factor"
)
)
"mdm" <- function(xold, types){
new("mdm", xold=xold, types=types)
}
setGeneric("head",function(x,...){standardGeneric("head")})
setMethod("head",signature="mdm",function(x,n=6,...){
mdm(head(x at xold,n=n,...) , types=factor(head(x at types,n=n,...)))
} )
If the above lines are part of the package source, and I install the package
then sometimes I get errors like
> head(toy_mm())
Error in function (classes, fdef, mtable) :
unable to find an inherited method for function "head", for signature
"matrix"
>
and sometimes it works as desired.
Why should head() not be able to take the first few lines of a matrix?
It seems to be "forgetting" that head.matrix() exists.
Can anyone give me some pointers for debugging this problem?
rksh
--
Robin K. S. Hankin
Uncertainty Analyst
University of Cambridge
19 Silver Street
Cambridge CB3 9EP
01223-764877