[R] OOP and passing by value

[Philippe Grosjean]

I think you should be interested by section 5.4 (non-local assignments; 
closures) in Chamber's "Software for Data Analysis" book published in 
2008 by Springer 
(http://www.springer.com/statistics/computanional+statistics/book/978-0-387-75935-7).

Besides the solution proposed in the book, which uses assignment outside 
functions, there is another possibility: environment objects. They are 
passed by reference and there are tricks to use them in this situation, 
but you have to be extremely careful because you break the rules for 
functional programming.

Don't forget generics like "Data<-" to assign in R. See for instance 
help("names<-"). This is the most conventional and easier way to do this.

Best,

Philippe Grosjean

On 09/06/10 14:28, michael meyer wrote:
> Greetings,
>
> I love the R system and am sincerely grateful for the great effort the
> product and contributors
> are delivering.
>
> My question is as follows:
>
> I am trying to use S4 style classes but cannot write functions that modify
> an object
> because paramter passing is by value.
> For example I want to do this:
>
> setGeneric("setData", function(this,fcn,k){ standardGeneric("setData") })
>
> setClass(
>    "test",
>    representation(f="numeric", t="numeric")
> )
> setMethod("setData","test",
>    function(this,fcn,k){
>      this at t<- as.numeric(seq(-k,k))/(2*k+1)
>      this at f<- sapply(t,FUN=fcn)
>    }
> )
>
> #-----------------------------------------------------------
> tst<- new("test")
> fcn<- function(u){ sin(2*pi*u) }
> setData(tst,fcn,100)
> tst at t   # it's still empty because of pass by value
>
>
> How can this be handled?
>
>
> Many thanks,
>
> Michael
>
> 	[[alternative HTML version deleted]]
>
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