[Rd] Writing new methods for `names<-`

[Martin Morgan]

On 11/02/2011 11:57 AM, Max Gasner wrote:
> Hi there,
>
> I'm working with an object whose internal data representation is very
> different from a data.frame (data is stored as a list of big.matrix objects
> from the bigmemory package) but to which I'd like to give users
> data.frame-like access. I've implemented names very easily as follows:
>
> setMethod("names", signature = "my.dataset", definition = function (x) {
>    x at colnames
> })
>
> Now I'd like to implement `names<-` analogously.
>
> Of course the following does not work, because only the local copy of the
> dataset is changed:
>
> setMethod("names<-", signature = "my.dataset", definition = function (x,
> value) {
>    x at colnames<- value
> })
>
> Following a suggestion I found in the list archives, I thought it might be
> worthwhile to try something like the following:
>
> setMethod("names<-", signature = "my.dataset", definition = function (x,
> value, env = parent.frame()) {
>    with(parent.frame(), x at colnames<- value)
> })
>
> But of course because `names<-` is primitive, if I try to redefine the
> generic function as follows so I can pass it another argument:
>
> setGeneric("names<-", def = function (x, value, ...) {
> standardGeneric("names<-") })
>
> Then I get the following error:
>
> Error in setGeneric("names<-", def = function(x, value, ...) { :
>    ‘names<-’ is a primitive function;  methods can be defined, but the
> generic function is implicit, and cannot be changed.
>
> Any advice on ways around this, or other approaches to the problem, would
> be very welcome!

Hi Max --

'names<-' is already a generic

 > getGeneric("names<-")
standardGeneric for "names<-" defined from package "base"

function (x, value)
standardGeneric("names<-", .Primitive("names<-"))
<environment: 0x8f0a48>
Methods may be defined for arguments: x, value
Use  showMethods("names<-")  for currently available ones.

so write a 'replacement' method

setReplaceMethod("names", "my.dataset", function(x, value) {
     x at colnames <- value
     x
})

Hope that helps,

Martin

>
> Thanks,
>
> Max
>
>
>
> Max Gasner
> Navia Systems | 415 413 3821
>
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>
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>
>
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