Thank you very much, Martin. :)
b
On Oct 14, 2009, at 5:23 PM, Martin Morgan wrote:
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
______________________________________________
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.
