[R] passing an extra argument to an S3 generic

[Michael Friendly]

On 2/11/2012 12:00 PM, ilai wrote:
> You are setting a new class ("inflmlm") at the end of mlm.influence.
> Remove that second to last line and enjoy your new S3 method.

Thanks for the suggestion, but it doesn't help -- I still get the same
behavior whether mlm.influence returns a classed object or not.
As well, I am defining print.inflmlm() and as.data.frame.inflmlm() 
methods for these objects, so I do need mlm.influence to return a 
classed object.

My hatvalues.mlm is designed to be similar in structure to 
stats::hatvalues.lm where the S3 generic is defined.

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
}

 > hatvalues
function (model, ...)
UseMethod("hatvalues")
<bytecode: 0x0326fd30>
<environment: namespace:stats>
 > hatvalues.lm
function (model, infl = lm.influence(model, do.coef = FALSE),
     ...)
{
     hat <- infl$hat
     names(hat) <- names(infl$wt.res)
     hat
}
<bytecode: 0x0326de6c>
<environment: namespace:stats>

The idea is that the infl= argument specifies a call to the 
computational function, mlm.influence() in my case, just as 
lm.influence() does in the stats package.

The logic of UseMethod is that it should dispatch on the class of the 
*first* argument to the function, which in my test case is c("mlm", "lm")

 > Rohwer.mod <- lm(cbind(SAT, PPVT, Raven) ~ n+s+ns+na+ss, data=Rohwer2)
 > class(Rohwer.mod)
[1] "mlm" "lm"

 > trace(hatvalues)
 > hatvalues(Rohwer.mod, m=2)
trace: hatvalues(Rohwer.mod, m = 2)
Error in UseMethod("hatvalues") :
   no applicable method for 'hatvalues' applied to an object of class 
"c('double', 'numeric')"
 > hatvalues(Rohwer.mod)
trace: hatvalues(Rohwer.mod)
          1          2          3          4          5          6 
     7          8
0.16700926 0.21845327 0.14173469 0.07314341 0.56821462 0.15432157 
0.04530969 0.17661104
...


I'm still stumped on why with the extra argument m=2, R sees this
as an object of class c('double', 'numeric').  As well, I can't see
any way to debug this.


> I'm not sure, but I think it is just the new class "inflmlm" applied
> to inf in the formals of hatvalues.mlm confused the dispatch
> mechanism. You would think the error message will call the offending
> class not "numeric" double" but that's above my pay grade...
>
> You could probably put back the inflmlm class assignment with an
> explicit call to UseMethod in hatvalues.mlm ?
>
> Cheers
>
> On Fri, Feb 10, 2012 at 2:35 PM, Michael Friendly<friendly at yorku.ca>  wrote:
>> On 2/10/2012 4:09 PM, Henrik Bengtsson wrote:
>>>
>>> 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
>>> }
>>
>> Thanks;  I tried exactly that, but I still can't pass m=2 to the mlm method
>> through the generic
>>
>>> hatvalues(Rohwer.mod)
>>          1          2          3          4          5          6          7
>>           8
>> 0.16700926 0.21845327 0.14173469 0.07314341 0.56821462 0.15432157 0.04530969
>> 0.17661104
>>          9         10         11         12         13         14         15
>>          16
>> 0.05131298 0.45161152 0.14542776 0.17050399 0.10374592 0.12649927 0.33246744
>> 0.33183461
>>         17         18         19         20         21         22         23
>>          24
>> 0.17320579 0.26353864 0.29835817 0.07880597 0.14023750 0.19380286 0.04455330
>> 0.20641708
>>         25         26         27         28         29         30         31
>>          32
>> 0.15712604 0.15333879 0.36726467 0.11189754 0.30426999 0.08655434 0.08921878
>> 0.07320950
>>
>>> hatvalues(Rohwer.mod, m=2)
>> Error in UseMethod("hatvalues") :
>>   no applicable method for 'hatvalues' applied to an object of class
>> "c('double', 'numeric')"
>>
>> ## This works:
>>> hatvalues.mlm(Rohwer.mod, m=2)
>>    ... output snipped
>>
>>> hatvalues
>>
>> function (model, ...)
>> UseMethod("hatvalues")
>> <bytecode: 0x021339e4>
>> <environment: namespace:stats>
>>
>>>
>>
>> -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
>>
>>
>


-- 
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