R help - Mar 2006 - Class & Method, S3 / S4

Hi

I'm trying to create a class. However, I've some problems...

I am used to program php. There I can create a new object and call a specific
function of this object. In R, I hoped to create a class similar and then
call the function like:

Creating the Class:
<CODE>-----------------------------------
setClass("connect",
		representation(test="function"))
)

setMethod("test", "connect", 
    function(value){ 
        value /2
	}
)
</CODE>-----------------------------------


testObj = new ("connect")
testObj at test(44)

That should return 22. However, unfortunately it does not work. How can I
solve this problem. I read several instructions, but how does R work???.
Does anybody have a very simple example like above.

I highly appreciate any help.
Thanks a lot.
Nik

The object paradigm in R is different; I like to think of methods as
orthogonal to classes, instead of nested within them.

Probably what you want to try is

# a generic function, to operate on different classes
setGeneric("test", function( obj ) standardGeneric( "test"
))

# a class, containing data
setClass("connect", representation( value = "numeric" ))

# a specific method, operating on "connect" objects
setMethod("test", signature=c("connect"),
  function( obj ) { obj at value / 2 })

# a new object of class "connect" with value slot assigned 44
testObj <- new("connect", value=44 )
# application of the generic function to an object of class "connect",
# dispatched to the method operating on objects of class "connect"
test( testObj )  

This kind of structuure makes some types of operations particularly
natural in R -- dispatch on multiple arguments, for instance.

Hope that helps,

Martin


mailto-nik at bluemail.ch writes:
> Hi
>
> I'm trying to create a class. However, I've some problems...
>
> I am used to program php. There I can create a new object and call a
specific
> function of this object. In R, I hoped to create a class similar and then
> call the function like:
>
> Creating the Class:
> <CODE>-----------------------------------
> setClass("connect",
> 		representation(test="function"))
> )
>
> setMethod("test", "connect", 
>     function(value){ 
>         value /2
> 	}
> )
> </CODE>-----------------------------------
>
>
> testObj = new ("connect")
> testObj at test(44)
>
> That should return 22. However, unfortunately it does not work. How can I
> solve this problem. I read several instructions, but how does R work???.
> Does anybody have a very simple example like above.
>
> I highly appreciate any help.
> Thanks a lot.
> Nik
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

Hi Martin

Thanks a lot for your short example. If you input

test(testObj)

it will return

22

However, how is it possible that the value will be saved in the object

i.e. (does not work currently!!??)
setMethod("test", signature=c("connect"),
  function( obj ) { obj at value<-obj at value / 2 })

so that test(testObj) will save a new value to obj at value or 

testObj at value will return 22.

Thanks.
Nik