[R] Cacheing computationally expensive getter methods for S4 objects

[Steve Lianoglou]

Very clever, that looks to do the trick!

Thanks,

-steve

On Oct 14, 2009, at 2:57 PM, Benilton Carvalho wrote:

> If you change 'area' to an environment, you may be able to get  
> something close to what you want.
>
> For example:
>
> setClass("Square",
>         representation(
>                        length='numeric',
>                        width='numeric',
>                        area='environment'
>                        ),
>         prototype(
>                   length=0,
>                   width=0,
>                   area=new.env()
>                   )
>         )
>
> setGeneric("area", function(x) standardGeneric("area"))
> setMethod("area", "Square",
>          function(x){
>            if (length(ls(x at area)) == 0){
>              message("Computing")
>              assign("area", x at width * x at length, envir=x at area)
>            }
>            message("Accessing")
>            get("area", envir=x at area)
>          })
>
> tmp <- new("Square", length=5, width=10)
> area(tmp) ## This should show "computing" and "accessing"
> area(tmp) ## the 2nd call should show 'accessing' only
>
>
> b
>
>
>
> On Oct 14, 2009, at 3:31 PM, Steve Lianoglou wrote:
>
>> Hi,
>>
>> I was wondering if there was a way to store the results of a
>> computationally expensive "getter" call on an S4 object, so that it  
>> is
>> only calculated once for each object.
>>
>> Trivial example: let's say I want to cache the "expensive" area
>> calculation of a square object.
>>
>> setClass("Square",
>>  representation(
>>    length='numeric',
>>    width='numeric',
>>    area='numeric'
>>  ),
>>  prototype(
>>    length=0,
>>    width=0,
>>    area=-1
>>  )
>> )
>>
>> setGeneric("area", function(x) standardGeneric("area"))
>> setMethod("area", "Square",
>> function(x) {
>>  if (x at area == -1) {
>>    x at area <- x at width * x at height
>>  }
>>  x at area
>> })
>>
>> Now the first time I call ``area(my.square)`` it computes
>> ``my.square at width * my.square at height``, but each subsequent call
>> returns ``x at area`` since the area computation has already been calc'd
>> and set for this object.
>>
>> Is this possible? I'm guessing the R pass by value semantics is going
>> to make this one difficult ... is there some S4 reference I missed
>> that has this type of info from?
>>
>> Thanks,
>> -steve
>>
>> --
>> Steve Lianoglou
>> Graduate Student: Computational Systems Biology
>>  |  Memorial Sloan-Kettering Cancer Center
>>  |  Weill Medical College of Cornell University
>> Contact Info: http://cbio.mskcc.org/~lianos/contact
>>
>> ______________________________________________
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>

--
Steve Lianoglou
Graduate Student: Computational Systems Biology
   |  Memorial Sloan-Kettering Cancer Center
   |  Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact