[Rd] S4: what to put in initialize, validity and constructor?

[cgenolin at u-paris10.fr]

> Do not change initialize!

As I sat, this is a toy example. In my real example, initialize does a 
lot of things like calculation of quality indice (b is not the scare of 
a, but B1, B2 and B3 are the the within matrix of A after imputation 
with 3 differents methods), giving names to some matrix column and so 
on. So I seams costfull to not use an initialize.

> Define constructors:
>
> setGeneric("A", function(a,b,...) standardGeneric("A"))
>
> setMethod("A", signature(a="missing",b="missing"),
>  function(a,b,...) A(as.numeric(1:10),...) ## calls the one below
> )
>
> setMethod("A", signature(a="A",b="missing"),
>  function(a,b,...) a
> )
>
> setMethod("A", signature(a="ANY",b="ANY"),
>  function(a,b,...) new("A",a=as.numeric(a),b=as.numeric(b),...)
> )
>
> setMethod("A", signature(a="ANY",b="missing"),
>  function(a,b,...) A(a,a,...) ## Calls the one above
> )
>
> etc.
>
> In words:
> 1) validity should return a character in case of errors
> 2) default initializer usually does the job
> 3) define constructors as methods to allow different signatures and
>   conversions from other classes
> 4) If you derive your class from numeric, rather than add slots,
>   the performance will be much better and you will get default
>   behaviour of numeric, i.e.
>
> setClass("A",
>  representatiom("numeric", b="numeric") etc
>
> Dr Oleg Sklyar
> Technology Group
> Man Investments Ltd
> +44 (0)20 7144 3803
> osklyar at maninvestments.com
>
>> -----Original Message-----
>> From: r-devel-bounces at r-project.org
>> [mailto:r-devel-bounces at r-project.org] On Behalf Of
>> cgenolin at u-paris10.fr
>> Sent: 02 May 2008 15:41
>> To: r-devel at r-project.org
>> Subject: [Rd] S4: what to put in initialize, validity and constructor?
>>
>> Hi the list,
>>
>> I have some trouble using validity, intialize and the
>> constructor. More precisely, what should go where?
>> Here is a toy exemple (seams long, but the code is very simple):
>>
>> I want to define an object with two slots a and b with the
>> properties that b will be either empty or the scare of a.
>> Example of valid object :
>>   a=  b=
>>   a=2 b=
>>   a=3 b=9
>>
>> So I define my object and the validity function :
>>
>> setClass(
>>     "A",
>>     representation(a="numeric",b="numeric"),
>>     validity=function(object){
>>         cat("Validity\n")
>>         if(length(object at b)!=0){
>>             if(length(object at a)==0){stop("Can not have empty
>> a and non emty b")}else{}
>>             if(object at a^2!=object at b){stop("b is not the scare
>> of a")}else{}
>>         }else{}
>>         return(TRUE)
>>     }
>> )
>>
>> It works:
>>
>> new("A")
>> new("A",a=2,b=4)
>> try(new("A",b=4))
>> new("A",a=2)
>> try(new("A",a=2,b=3))
>>
>>
>> Then I define the initialize function. When b is givent but
>> not a, the initialise function set a to sqrt(b).
>>
>> setMethod(
>>     "initialize",
>>     "A",
>>     function(.Object,a,b){
>>         if(missing(a)&!missing(b)){
>>             .Object at b <- b
>>             .Object at a <- sqrt(b)
>>         }else{}
>>         if(!missing(a)&missing(b)){
>>             .Object at a <- a
>>         }else{}
>>         if(!missing(a)&!missing(b)){
>>             .Object at a <- a
>>             .Object at b <- b
>>         }else{}
>>         validObject(.Object)
>> 	return(.Object)
>>     }
>> )
>>
>> It is fine:
>>
>> new("A")
>> new("A",a=2,b=4)
>> new("A",b=9)
>> new("A",a=2)
>> try(new("A",a=2,b=3))
>>
>>
>> Then I want to set the constructor
>>
>> A <- function(a,b){
>>     return(new("A",a,b))
>> }
>>
>> But this does not work:
>> A()
>> A(a=2,b=4)
>> A(b=9)
>> A(a=2)
>>
>>
>> The following does not work either:
>>
>> A <- function(a=numeric(),b=numeric()){
>>     return(new("A",a,b))
>> }
>>
>> A()
>> A(a=2,b=4)
>> A(b=9)
>> A(a=2)
>>
>> So is there a way to define the constructor A without dealing
>> again with all the missing&missing staff like in initialize?
>>
>> Christophe
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
>
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