[R] passing an extra argument to an S3 generic

[Henrik Bengtsson]

For these type of setups, I typically turn to "default" values, e.g.

hatvalues.mlm <- function(model, m=1, infl=NULL, ...)
{
   if (is.null(infl)) {
     infl <- mlm.influence(model, m=m, do.coef=FALSE);
   }

   hat <- infl$H
   m <- infl$m
   names(hat) <- if(m==1) infl$subsets else apply(infl$subsets,1,
paste, collapse=',')
   hat
}

So people may prefer to do the following:

hatvalues.mlm <- function(model, m=1, infl, ...)
{
   if (missing(infl)) {
     infl <- mlm.influence(model, m=m, do.coef=FALSE);
   }

   hat <- infl$H
   m <- infl$m
   names(hat) <- if(m==1) infl$subsets else apply(infl$subsets,1,
paste, collapse=',')
   hat
}

The downside with this approach is that args(<fcn>) doesn't reveal the
default behavior; instead you need to document it clearly in the
help(<fcn>).

My $.02

/H

On Fri, Feb 10, 2012 at 12:13 PM, Michael Friendly <friendly at yorku.ca> wrote:
> On 2/9/2012 6:24 PM, ilai wrote:
>>
>> You do not provide mlm.influence() so your code can't be reproduced.
>>
>> Or did you mean to put lm.influence() in the formals to your hatvalues.mlm
>> ?
>>
>> If yes, then 1) you have a typo 2) lm.influence doesn't allow you to
>> pass on arguments, maybe try influence.lm instead.
>
>
> No, I've written an S3 method, influence.mlm and a computational method,
> mlm.influence, both of which take an m= argument.  I didn't post all the
> code because I thought the question might have an easy answer based on what
> I provided.
>
> I include all the code and a test case in the attached .txt file that
> can be sourced.
>
> -Michael
>
>
>>
>> Elai
>>
>> On Thu, Feb 9, 2012 at 1:42 PM, Michael Friendly<friendly at yorku.ca>
>>  wrote:
>>>
>>> I'm trying to write some functions extending influence measures to
>>> multivariate linear models and also
>>> allow subsets of size m>=1 to be considered for deletion diagnostics.
>>>  I'd
>>> like these to work roughly parallel
>>> to those functions for the univariate lm where only single case deletion
>>> (m=1) diagnostics are considered.
>>>
>>> Corresponding to stats::hatvalues.lm, the S3 method for class "lm"
>>> objects,
>>>
>>>> hatvalues<-function (model, ...)
>>>
>>> UseMethod("hatvalues")
>>>
>>>> hatvalues.lm<-
>>>
>>> function (model, infl = lm.influence(model, do.coef = FALSE),    ...)
>>> {
>>>    hat<- infl$hat
>>>    names(hat)<- names(infl$wt.res)
>>>    hat
>>> }
>>>
>>> I have, for class "mlm" objects
>>>
>>> hatvalues.mlm<- function(model, m=1, infl=mlm.influence(model, m=m,
>>> do.coef
>>> = FALSE), ...)
>>> {
>>>    hat<- infl$H
>>>    m<- infl$m
>>>    names(hat)<- if(m==1) infl$subsets else apply(infl$subsets,1, paste,
>>> collapse=',')
>>>    hat
>>> }
>>>
>>> where mlm.influence() does the calculations, but also allows the m=
>>> argument
>>> to specify subset size.
>>> Yet when I test this I can't seem to pass the m= argument directly, so
>>> that
>>> it gets stuffed in to the infl=
>>> call to mlm.influence.
>>>
>>> # fit an mlm
>>> library(heplots)
>>> Rohwer2<- subset(Rohwer, subset=group==2)
>>> rownames(Rohwer2)<- 1:nrow(Rohwer2)
>>> Rohwer.mod<- lm(cbind(SAT, PPVT, Raven) ~ n+s+ns+na+ss, data=Rohwer2)
>>>
>>>> class(Rohwer.mod)
>>>
>>> [1] "mlm" "lm"
>>>
>>>
>>> ## this doesn't work, as I would like it to, calling the hatvalues.mlm
>>> method, but passing m=2:
>>>>
>>>> hatvalues(Rohwer.mod, m=2)
>>>
>>> Error in UseMethod("hatvalues") :
>>>  no applicable method for 'hatvalues' applied to an object of class
>>> "c('double', 'numeric')"
>>>
>>> I don't understand why this doesn't just call hatvalues.mlm, since
>>> Rohwer.mod is of class "mlm".
>>>
>>> # These work -- calling hatvalues.mlm explicitly, or passing the infl=
>>> argument with the call to
>>> # mlm.influence
>>>>
>>>> hatvalues.mlm(Rohwer.mod, m=2)
>>>> hatvalues(Rohwer.mod, infl=mlm.influence(Rohwer.mod,m=2))
>>>
>>>
>>> Can someone help me understand what is wrong and how to make the .mlm
>>> method
>>> allow m= to be passed
>>> directly to the infl= computation?
>>>
>>> thx,
>>> -Michael
>>>
>>> --
>>> Michael Friendly     Email: friendly AT yorku DOT ca
>>> Professor, Psychology Dept.
>>> York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
>>> 4700 Keele Street    Web:   http://www.datavis.ca
>>> Toronto, ONT  M3J 1P3 CANADA
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>
>
> --
> Michael Friendly     Email: friendly AT yorku DOT ca
> Professor, Psychology Dept.
> York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
> 4700 Keele Street    Web:   http://www.datavis.ca
> Toronto, ONT  M3J 1P3 CANADA
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>