[R] NextMethod() example from S Programming by Venables and Ripley (page 78)

[Ken Knoblauch]

blue sky <bluesky315 <at> gmail.com> writes:
> S Programming by Venables and Ripley (page 78) has the example listed
> at the end of this email. However, I get the following error when I
> try the example. I don't understand the descriptions of NextMethod on
> its help page. Could somebody let me know how to fix the error of this
> example?
> > test(x)
> c1
> c2
> Error in NextMethod() : no method to invoke
> Calls: test -> test.c1 -> NextMethod -> test.c2 -> NextMethod
> Execution halted
> 
> ####
> test=function(x) UseMethod('test')
> 
> test.c1=function(x) {
>   cat('c1\n')
>   NextMethod()
>   x
> }
> 
> test.c2=function(x) {
>   cat('c2\n')
>   NextMethod()
>   x
> }
> 
> test.c3=function(x) {
>   cat('c3\n')
>   x
> }
> 
> x=1
> class(x)=c('c1','c2')
> test(x)
It works fine for me if you add a default method,
which I think is what it is looking for. 

test.default <- function(x){
cat("default")
x
}

 test(x)
c1
c2
default[1] 1
attr(,"class")
[1] "c1" "c2"



-- 
Ken Knoblauch
Inserm U846
Stem-cell and Brain Research Institute
Department of Integrative Neurosciences
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