Re: [Rd] Missing values for S4 slots [One Solution]

From: Martin Morgan <mtmorgan_at_fhcrc.org>
Date: Sat 25 Nov 2006 - 07:46:55 GMT

Ross Boylan <ross@biostat.ucsf.edu> writes:

> On Fri, Nov 24, 2006 at 11:23:14AM -0800, Ross Boylan wrote:
>> Using R 2.4, the following fails:
>> setClass("testc", representation(a="ANY"))
>> makeC <- function(myarg) new("testc", a=myarg)
>> makeC()
>> -> Error in initialize(value, ...) : argument "myarg" is missing,
>> with no default

The following might offer one paradigm:

makeC <- function(myarg) {

    new("testc",

        a=if (missing(myarg)) character(0) else myarg)     }

A couple of things that come to mind, though: 'ANY' kind of defeats the purpose of having a class with well-defined slots (I realize this is a 'toy' example); presenting myarg without a default makes it obscure to the user what the default value might be, or that a default value will be used; if 'myarg' is an appropriately descriptive argument for the user, then perhaps it is also appropriately descriptive for the slot. Thus:

setClass("testc",

         representation(myarg="character"))

makeC <- function(myarg=character(0)) new("testc", myarg=myarg)

> ....
>>
>> I suspect there's something I could do to get the constructor
>> arguments, modify the list (i.e., delete args that were missing and
>> insert new ones), and do.call(new, myArgList). Not only am I unsure
>> how to do that (or if it would work), I'm hoping there's a better way.
>
> I didn't find a way to get all the arguments easily(*), but manually

as.list(match.call()[-1]) might help

> constructing the list works. Here are fragments of the code:
>
> mspathCoefficients <- function(
> aMatrix,
> params,
> offset=0,
> baseConstrVec,
> covLabels # other args omitted
> ) {
> # innerArgs are used with do.call("new, innerArgs)
> innerArgs <- list(
> Class = "mspathCoefficients",
> aMatrix = aMatrix,
> baseConstrVec = as.integer(baseConstrVec),
> params = params
> )
>
> # the next block inserts the covLabels argument
> # only if it is non-missing
> if (missing(covLabels)) {
> # ....
> } else {
> innerArgs$covLabels <- covLabels
> }
> #...
> map <- list()
> # fill in the map
> # add it to the arguments
> innerArgs$map <- map
> do.call("new", innerArgs)
> }
>
> This calls new("mspathCoefficients", ...) with just the non-missing
> arguments. The constructed object has appropriately "missing" values
> in the slots (e.g., character(0) given a slot of type "character").
>
>
> (*) Inside the function, arg <- list(...) will capture the unnamed
> arguments, but I don't have any. as.list(sys.frame(sys.nframe()) is
> closer to what I was looking for, though all the values are promises.
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

-- 
Martin T. Morgan
Bioconductor / Computational Biology
http://bioconductor.org

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Received on Sat Nov 25 18:50:40 2006

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