Steve Lianoglou wrote:
> Very clever, that looks to do the trick!
I think though that all Square's then share the same environment
(created in the prototype) and hence area.
> area(new("Square", length=50, width=100))
Accessing
[1] 50
Which is quite efficient at doing the calculation, but maybe not what is
expected...
The solution is to create the area environment in an 'initialize' method.
A different approach, but along similar lines, might make 'area' a
function that exploits lexical scope. Here's an area 'factory'
areaf <- function() {
area <- NULL
function(x) {
if (is.null(area)) {
message("expensive")
area <<- x...@length * x...@width
}
area
}
}
that we use in the initialize method
setMethod(initialize, "Rect",
function(.Object, ..., length=.obj...@length,
width=.obj...@width)
{
callNextMethod(.Object, area=areaf(), length=length,
width=width, ...)
})
setMethod(area, "Rect", function(x) x...@area(x))
The signature of initialize is such that one could
setReplaceMethod("length", c("Rect", "numeric"), function(x, value) {
initialize(x, length=value)
})
so
> a <- new("Rect", length=10, width=5)
> area(a)
expensive
[1] 50
> area(a) # cheap
[1] 50
> b <- a
> area(b)
[1] 50
> length(b) <- 20
> area(a)
[1] 50
> area(b)
expensive
[1] 100
Martin
>
> 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...@area)) == 0){
>> message("Computing")
>> assign("area", x...@width * x...@length, envi...@area)
>> }
>> message("Accessing")
>> get("area", envi...@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...@area == -1) {
>>> x...@area <- x...@width * x...@height
>>> }
>>> x...@area
>>> })
>>>
>>> Now the first time I call ``area(my.square)`` it computes
>>> ``my.squ...@width * my.squ...@height``, but each subsequent call
>>> returns `...@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
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> 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
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
--
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109
Location: Arnold Building M1 B861
Phone: (206) 667-2793
______________________________________________
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