From jmc at r-project.org  Thu Apr 21 22:36:00 2011
From: jmc at r-project.org (John Chambers)
Date: Thu, 21 Apr 2011 13:36:00 -0700
Subject: [Rd] problem subsetting of a reference class
In-Reply-To: <1303413851743-3466690.post@n4.nabble.com>
References: <1303413851743-3466690.post@n4.nabble.com>
Message-ID: <4DB09530.9010005@r-project.org>

You're confusing functional and OOP-style methods.

Since you define an OOP-style method, you need to invoke it in OOP style.

With your example:


 > tmp$`[`("random")
  [1] -1.439131143 -0.630354726  0.822006263 -0.651707539  0.475332681
  [6]  0.002680224  1.539035675 -0.117609566  2.066227300  1.111270997
 >


You could if you wanted define a functional method via setMethod() to 
allow functional access, by invoking the $`[`() method--preferably after 
changing its name.  It's probably a matter of opinion whether that's a 
good use of OOP-style methods.


On 4/21/11 12:24 PM, A Zege wrote:
> I am trying to define subset operator for a reference class and hitting some
> problem i am unable to diagnose.To give an example, here is a toy class
> generator that is a wrapper around a list
>
>
>
>
> tmpGEN<-setRefClass("TMP", fields=list(
> 				namelist="list"
> 		))
> tmpGEN$methods('add'=function(obj, name){
> 	namelist[[name]]<<-obj
> })
>
> tmpGEN$methods('['=function(name){
> 			if(class(name)!="character")
> 				stop('to return cache element need to pass its name')
> 			ind<-match(name, names(namelist))
> 			if(is.na(ind))
> 				stop('data to remove is not in namelist')
> 			namelist[[name]]
> 		})
>
>
> ==============
>
> when i try to use it, the following happens
> v<-rnorm(10)
> tmp<-tmpGEN$new()
> tmp$add(v, 'random')
>
> ..... up until here everything is ok, class is generated and vector is
> added. Now when i do
> tmp['random']
>
> i get error message
>
> Error in tmp["random"] : object of type 'S4' is not subsettable
>
> Not sure if it means that i cannot define "[" operator for a class or if i
> am doing it syntactically wrong
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/problem-subsetting-of-a-reference-class-tp3466690p3466690.html
> Sent from the R devel mailing list archive at Nabble.com.
>
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[Rd] problem subsetting of a reference class
John Chambers