Hadley,
thanks for your comment. What you're saying is true, of course, and possibly
I did not really chose the best header to describe the actual issue I was
addressing. However, in the help archive I found something that gets me what
I want (calling a certain "slot function" without having to specify
arguments at calling time). I adapted it to my situation and maybe it's of
interest for someone facing a similar problem.
setClass(
Class="Testclass",
representation=representation(
env="environment",
data="function"
)
)
data.fun <- function(env) get("actual.data", env=env)
setMethod(
f="initialize",
signature=signature("Testclass"),
definition=function(
.Object,
actual.data=NULL,
...
) {
env <- new.env(parent=emptyenv())
env$actual.data <- actual.data
data.fun.wrapper <- function() data.fun(env)
callNextMethod(.Object, env=env, data=data.fun.wrapper, ...)
}
)
obj <- new("Testclass", actual.data=1:10)
o...@data()
o...@env$actual.data <- 1:5
o...@data()
obj.mod <- new("Testclass")
obj....@env$actual.data <- "horst"
obj....@data()
Loading an object from harddrive could be implemented in a similar way by
putting the path-filename-combination in "o...@env" and adapting the function
"data.fun()" accordingly.
Putting "data.fun()" into the wrapper "data.fun.wrapper()" allows for
changes in "data.fun()" without having to re-source the method for
"initialize()" and to reassign "obj" each time.
Regards,
Janko
> -----Ursprüngliche Nachricht-----
> Von: hadley wickham [mailto:h.wick...@gmail.com]
> Gesendet: Freitag, 15. Januar 2010 19:35
> An: Janko Thyson
> Cc: r-help@r-project.org
> Betreff: Re: [R] Can an object reference itself?
>
> On Fri, Jan 15, 2010 at 5:30 PM, Janko Thyson
> <janko.thy...@ku-eichstaett.de> wrote:
> > Dear List,
> >
> > I am not really familiar with any other language than R, but Ive
> heard that
> > in other languages there is something called self referencing.
> >
> > Heres what Im trying to get an answer for:
> > Suppose there is a function that takes as its input a value of a slot
> of an
> > S4 object. The function itself is stored in another slot of the SAME
> S4
> > object. Is it then possible to have the function automatically
> recognize
> > the name of the object in which slot it is placed via some sort of
> self
> > referencing of the S4 object (to avoid having to explicitly state
> the
> > required function argument for different S4 object instances with
> different
> > names)?
> >
> > I hope the following code snippets will give you an idea what Im
> trying to
> > do:
> >
> > obj.for.slot <- data.frame(a=1); obj.for.slot <- data.frame(a=100)
> > save(obj.for.slot, file="C:/obj.1.for.slot.Rdata");
> save(obj.for.slot,
> > file="C:/obj.2.for.slot.Rdata")
> >
> > slotfun <- function(obj.name)
> > {
> > file.fqn.char <- paste("file.fqn <- ", obj.name, "@file.fqn",
> > sep="")
> > eval(parse(text=file.fqn.char))
> > load(file=file.fqn)
> > return(obj.for.slot)
> > }
> >
> > setClass(
> > Class="Testclass",
> > representation=representation(
> > file.fqn="character",
> > data="function"
> > ),
> > prototype=prototype(
> > file.fqn="blabla",
> > data=slotfun
> > )
> > )
> >
> > test <- new("Testclass")
> > test.mod <- new("Testclass")
> >
> >
> > t...@file.fqn <- "C:/obj.1.for.slot.Rdata"
> > test....@file.fqn <- "C:/obj.2.for.slot.Rdata"
> >
> > t...@data(obj.name="test")
> > test....@data(obj.name="test.mod")
>
> An object does not have a unique name. What would happen in the
> following situations?
>
> t3 <- test.mod
> tests <- list(
> test,
> test.mod
> )
>
> Hadley
>
> --
> http://had.co.nz/
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