Dear Developers,
callNextMethods does not work with "$"
setClass("mylist", contains = "list"):
setMethod("$",
signature(x = "mylist"),
function (x, name){
cat("here:\n")
callNextMethod()
})
tl <- new("mylist")
tl[["x"]] <- 343
tl$x
#here:
#NULL
If I use callNextMethod(x=x, name=name)
this error is issued:
Error in function (classes, fdef, mtable) :
unable to find an inherited method for function "addNextMethod", for
signature "function"
It must be something "$" specific. If the above is an expected
behavior , how
should I call next method for "$" generic?
My info:
R version 2.12.0 Patched (2010-11-01 r53513)
Platform: i386-pc-mingw32/i386 (32-bit)
Same behavior for official R 2.12.0.
Thanks,
Vitalie.
The problem here is that the primitive for `$` does not use standard R
evaluation on its second argument, so when it is selected as the next
method the call is effectively x$name regardless of the original call.
If possible, I would avoid such cascaded calls of methods for `$`,
precisely because of the nonstandard evaluation, which makes the
interpretation of each level of the call ambiguous.
If this kind of code is needed, then the primitive method should get a
call in which the literal name is in place and the object has been
coerced suitably.
In this example, something like
> setMethod("$", "mylist", function(x, name) {
+ theName <- substitute(name)
+ expr <- substitute(xx$NAME, list(NAME = theName))
+ xx <- unclass(x)
+ eval(expr)
+ })
[1] "$"
> tl <- new("mylist")
> tl[["z"]] <- 1
> tl$z
[1] 1
On 11/10/10 4:49 AM, Vitalie S. wrote:> Dear Developers,
>
> callNextMethods does not work with "$"
>
> setClass("mylist", contains = "list"):
> setMethod("$",
> signature(x = "mylist"),
> function (x, name){
> cat("here:\n")
> callNextMethod()
> })
>
> tl<- new("mylist")
> tl[["x"]]<- 343
>
> tl$x
> #here:
> #NULL
>
>
> If I use callNextMethod(x=x, name=name)
>
> this error is issued:
>
> Error in function (classes, fdef, mtable) :
> unable to find an inherited method for function
"addNextMethod", for signature "function"
>
> It must be something "$" specific. If the above is an expected
behavior , how
> should I call next method for "$" generic?
>
> My info:
> R version 2.12.0 Patched (2010-11-01 r53513)
> Platform: i386-pc-mingw32/i386 (32-bit)
>
> Same behavior for official R 2.12.0.
>
> Thanks,
> Vitalie.
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
John Chambers <jmc4 at stanford.edu> writes:> The problem here is that the primitive for `$` does not use standard R > evaluation on its second argument, so when it is selected as the next method > the call is effectively x$name regardless of the original call. > > If possible, I would avoid such cascaded calls of methods for `$`, precisely > because of the nonstandard evaluation, which makes the interpretation of each > level of the call ambiguous. > > If this kind of code is needed, then the primitive method should get a call > in which the literal name is in place and the object has been coerced > suitably. > > In this example, something like > >> setMethod("$", "mylist", function(x, name) { > + theName <- substitute(name) > + expr <- substitute(xx$NAME, list(NAME = theName)) > + xx <- unclass(x) > + eval(expr) > + }) > [1] "$" >> tl <- new("mylist") >> tl[["z"]] <- 1 >> tl$z > [1] 1Thank you, that helps.> > On 11/10/10 4:49 AM, Vitalie S. wrote: >> Dear Developers, >> >> callNextMethods does not work with "$" >> >> setClass("mylist", contains = "list"): >> setMethod("$", >> signature(x = "mylist"), >> function (x, name){ >> cat("here:\n") >> callNextMethod() >> }) >> >> tl<- new("mylist") >> tl[["x"]]<- 343 >> >> tl$x >> #here: >> #NULL >> >> >> If I use callNextMethod(x=x, name=name) >> >> this error is issued: >> >> Error in function (classes, fdef, mtable) : >> unable to find an inherited method for function "addNextMethod", for > signature "function" >> >> It must be something "$" specific. If the above is an expected behavior , > how >> should I call next method for "$" generic? >> >> My info: >> R version 2.12.0 Patched (2010-11-01 r53513) >> Platform: i386-pc-mingw32/i386 (32-bit) >> >> Same behavior for official R 2.12.0. >> >> Thanks, >> Vitalie. >> >> ______________________________________________ >> R-devel at r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel>