R help - Jan 2010 - Can an object reference itself?

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")

I'm trying to have "slotfun()" be stated in a way that does not
require an
explicit stating of argument "obj.name"):
test at data()
test.mod at data()

Any hints in the right directions greatly appreciated!

Regards,
Janko Thyson

janko.thyson at kuei.de

Catholic University of Eichst?tt-Ingolstadt
Ingolstadt School of Management
Statistics and Quantitative Methods
Auf der Schanz 49
D-85049 Ingolstadt

www.wfi.edu/lsqm

Fon:? +49 841 937-1923
Fax:? +49 841 937-1965

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/