Sklyar, Oleg (MI London) wrote:
> Robin:
>
> two points:
> Second, your setReplaceMethod seems to be wrong in the definition, try the
> following adding signature for value and ... in the function call. You cannot
> simply drop the ... . Probably you will also need to include j="missing" in
> the signature. There is also no need to construct a new object on return and
> I do not think drop is a part of generic for replacement, it is for
> extraction though
>
> setReplaceMethod("[", signature(x="foo", value="ANY"),
> function(x, i,j, ..., recalculate=FALSE, value) {
> [EMAIL PROTECTED] = value
> if (recalculate) [EMAIL PROTECTED] = sum([EMAIL PROTECTED])
> x
> })
Informative to investigate this a bit further. Without the ... we have
> showMethods("[<-", class="foo", includeDef=TRUE)
Function: [<- (package base)
x="foo"
function (x, i, j, ..., value)
{
.local <- function (x, i, j, recalculate = FALSE, value)
x
.local(x, i, j, ..., value)
}
.local maps between the generic and the method signature; the map is
incorrect when there are additional arguments but no .... An
indiscretion, perhaps, on the part of the methods package. This is in
contrast to a method with ...
> showMethods("[<-", class="foo", includeDef=TRUE)
Function: [<- (package base)
x="foo"
function (x, i, j, ..., value)
{
.local <- function (x, i, j, ..., recalculate = FALSE, value)
x
.local(x, i, j, ..., value = value)
}
here .local plays the same role, but value is named explicitly and the
problem avoided.
With respect to use of 'new' and slot assignments, it might be delving
too much into implementation but I think (a) using 'initialize' is
better than 'new' when you're doing a copy construction and (b)
'initialize' is more memory efficient than slot assignment when doing
multiple assignments (at least tracemem says so):
setGeneric("up1", function(x) standardGeneric("up1"))
setGeneric("up2", function(x) standardGeneric("up2"))
setMethod("up1", signature(x="foo"), function(x) {
[EMAIL PROTECTED] <- 1
[EMAIL PROTECTED] <- NA_real_
x
})
setMethod("up2", signature(x="foo"), function(x) {
initialize(x, x=1, NC=NA_real_)
})
> a1 <- up1(a) # 2 copies
tracemem[0x6d08d60 -> 0x7fa4628]: up1 up1
tracemem[0x7fa4628 -> 0x9b45518]: up1 up1
> a2 <- up2(a) # just 1
tracemem[0x6d08d60 -> 0x6cad360]: initialize initialize up2 up2
> identical(a1, a2)
[1] TRUE
This also provides object validation, which may or may not be desirable.
Martin
> Here is the output:
>> a = new("foo", 1:15)
>> a
> An object of class “fooâ€
> [1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
> Slot "NC":
> [1] NA
>
>> a[5,recalculate=TRUE] = 25
>> a
> An object of class “fooâ€
> [1] 1 2 3 4 25 6 7 8 9 10 11 12 13 14 15
> Slot "NC":
> [1] 140
>
>
> Dr Oleg Sklyar
> Technology Group
> Man Investments Ltd
> +44 (0)20 7144 3803
> [EMAIL PROTECTED]
>
>> -----Original Message-----
>> From: [EMAIL PROTECTED]
>> [mailto:[EMAIL PROTECTED] On Behalf Of Robin Hankin
>> Sent: 02 April 2008 09:51
>> To: R-devel@r-project.org
>> Subject: [Rd] "[<-" plus drop-type extra argument
>>
>> Hello
>>
>> I am writing a replacement method for an S4 class and want to
>> pass an additional argument to "[<-"() along the lines of
>> "["()'s "drop"
>> argument.
>>
>> Specifically, I have an S4 class, call it "foo", with a slot 'x'
>> that is a
>> vector and a slot 'NC' that is a scalar.
>>
>> I want to be able to pass a Boolean argument to the
>> replacement method which specifies whether or not to
>> recalculate NC (which is time-consuming and often not
>> needed). I want the default behaviour to be "don't recalculate NC".
>>
>> Toy example follows, in which 'NC' is the sum of x (in my
>> application, calculating NC is an expensive multidimensional
>> integral).
>>
>>
>> setClass("foo",
>> representation = representation(x="numeric" , NC="numeric"),
>> prototype = list(x=double() , NC=NA_real_)
>> )
>>
>> setReplaceMethod("[",signature(x="foo"),
>> function(x,i,j,recalculate=FALSE,value){
>> jj <- [EMAIL PROTECTED]
>> jj[i] <- value
>> if(recalculate){
>> return(new("foo" , x=jj , NC=sum(jj)))
>> } else {
>> return(new("foo" , x=jj , NC=NA_real_))
>> }
>> }
>> )
>>
>>
>>
>>
>> Then
>>
>>
>>
>> >
>> > a <- new("foo", x=1:10,NC=45)
>>
>>
>> > a[4,recalculate=FALSE] <- 10000
>> > a
>> An object of class “foo”
>> Slot "x":
>> [1] 1 2 3 10000 5 6 7 8 9 10
>>
>> Slot "NC":
>> [1] NA
>>
>> # Desired behaviour: NC not recalculated
>>
>>
>> >
>> > a[4,recalculate=TRUE] <- 10000
>> > a
>> An object of class “foo”
>> Slot "x":
>> [1] 1 2 3 10000 5 6 7 8 9 10
>>
>> Slot "NC":
>> [1] 10051
>>
>>
>> # Desired behaviour: NC recalculated
>>
>> >
>> > a[4] <- 10000
>> Error in .local(x, i, j, ..., value) :
>> argument "value" is missing, with no default >
>>
>> # Undesired behaviour: I wanted 'recalculate' to take its
>> default value of FALSE, and 'NC' not be recalculated.
>>
>>
>> How to do this?
>>
>>
>>
>>
>>
>> --
>> Robin Hankin
>> Uncertainty Analyst and Neutral Theorist, National
>> Oceanography Centre, Southampton European Way, Southampton
>> SO14 3ZH, UK
>> tel 023-8059-7743
>>
>> ______________________________________________
>> R-devel@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
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