R devel - Nov 2011 - Writing new methods for `names<-`

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@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@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@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!

Thanks,

Max



Max Gasner
Navia Systems | 415 413 3821

	[[alternative HTML version deleted]]

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
>
> 	[[alternative HTML version deleted]]
>
>
>
>
> ______________________________________________
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> https://stat.ethz.ch/mailman/listinfo/r-devel

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