Message-ID: <001101ca986f$22cc5a10$68650e30$@thyson@ku-eichstaett.de>
Date: 2010-01-18T18:50:41Z
From: Janko Thyson
Subject: Can an object reference itself?
In-Reply-To: <f8e6ff051001151034o65fa7264vf02d4d3b6542a38b@mail.gmail.com>
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$actual.data <- actual.data
data.fun.wrapper <- function() data.fun(env)
callNextMethod(.Object, env=env, data=data.fun.wrapper, ...)
}
)
obj <- new("Testclass", actual.data=1:10)
obj at data()
obj at env$actual.data <- 1:5
obj at data()
obj.mod <- new("Testclass")
obj.mod at env$actual.data <- "horst"
obj.mod at data()
Loading an object from harddrive could be implemented in a similar way by
putting the path-filename-combination in "obj at 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
> -----Urspr?ngliche Nachricht-----
> Von: hadley wickham [mailto:h.wickham at gmail.com]
> Gesendet: Freitag, 15. Januar 2010 19:35
> An: Janko Thyson
> Cc: r-help at r-project.org
> Betreff: Re: [R] Can an object reference itself?
>
> On Fri, Jan 15, 2010 at 5:30 PM, Janko Thyson
> <janko.thyson at ku-eichstaett.de> wrote:
> > Dear List,
> >
> > I am not really familiar with any other language than R, but I?ve
> heard that
> > in other languages there is something called ?self referencing?.
> >
> > Here?s what I?m 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 I?m
> 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")
> >
> >
> > test at file.fqn ? ? ? ? ? <- "C:/obj.1.for.slot.Rdata"
> > test.mod at file.fqn ? ? ? <- "C:/obj.2.for.slot.Rdata"
> >
> > test at data(obj.name="test")
> > test.mod at 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/