On 04.06.2011, at 15:41, Martin Morgan wrote:
> On 06/04/2011 03:07 AM, soeren.vo...@uzh.ch wrote:
>
>> Hello, an S4 class "Foo" is defined with a setter, $. For several reasons,
>> the setter calls a function, .foo.update(). However, bypassing the argument
>> names of the setter does not work. Question 1: Why not and how can I fix
>> this? Question 2: What is the way to define either the function or the
>> setter to modify the original object (not returning the modified copy of it
>> an overwrite the original by assignment)? Thanks, Sören
>>
>> setClass("Foo",
>> representation(
>> N = "numeric"
>> ),
>> prototype(
>> N = 10000
>> )
>> )
>>
>> .foo.update<- function(object, ...) {
>> args<- list(...)
>> for (i in slotNames("Foo")[pmatch(names(args), slotNames("Foo"),
>> nomatch=0)]) {
>> slot(object, i)<- args[[i]]
>> # indeed more to do here
>> return(object)
>> }
>> }
>
> Since names(args) is 'name', and 'name' is not a slot of 'Foo', the return of
> pmatch is 0 and .foo.update returns NULL. Put return(object) outside the for
> loop.
>
>> setReplaceMethod("$", "Foo",
>> function(x, name, value) {
>> x<- .foo.update(x, name=value)
>> x
>> }
>> )
>>
>> x<- new("Foo")
>> x
>> x$N<- 99
>> x # NULL????
>
> here your intention is that name=value to be substituted with N=99, but you
> end up with name=99. You could arrange to parse this correctly, but this
> isn't usually what you _want_ to do and I don't really understand what you're
> trying to accomplish.
Exactly, what I want to parse is "N"=99. To clarify, .foo.update should be the
"one" workhorse to do a couple of things depending on arguments on more than
one object (see my post on interfacing a C++ class, just some minutes ago).
Thus, assigning x@N = 10 (x$N, x["N"]) should not only end up in x (object of
class Foo) with value 10, but also should invoke FOO$setN(10) (a setter for the
C++ object, not shown here). So far, .foo.update works perfectly and indeed
alters the object x, but the setter does not parse the argument name. I tried
with quote, substitute, deparse ..., but got none working ...
> Maybe
>
> .foo.update <- function(object, name, value, ...)
> {
> slot(object, name) <- value
> ## some other stuff
> object
> }
>
> Hope that helps a bit.
>
> Martin
Thanks, Sören
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