is.numeric(factor(...)) {was: bug in sample (PR#305)}

[Peter Dalgaard BSA]

Martin Maechler <maechler@stat.math.ethz.ch> writes:

> Before turning this into a new bug report (not connected to sample() at all):
> { factor() behavior redesigning must be done carefully... }
> Some detective work reveals
> 
> R versions from 0.50 to 0.61.3  all give
> 
>   is.numeric(gl(3,5,15)) 
> 			 |-> FALSE
> 
> Since R version 0.62.1 (June 15, 1998),
> the above gives TRUE.
>   
> The NEWS for 0.62[.1] has
> 
>     o	All internal mechanisms to support factors and data.frames have
> 	been removed.  These are now entirely supported by interpreted
> 	code!  `is.unordered' has been eliminated.  Thanks to John
> 	Chambers for allowing the distribution of his StatLib code.
> 
> i.e., they change occurded when we dropped the internal factor type...
> 
> --
> 
> Yes, my gut feeling also says that the current behavior is wrong...

We did have some debate over it at some point. The interesting thing
is that Splus has:

> mode(factor(letters[1:3]))
[1] "numeric"
> is.numeric(factor(letters[1:3]))
[1] F

> x<-1:3
> class(x)<-"foo"
> is.numeric(x)
[1] T
> attr(x,"levels")<-3:1
> is.numeric(x)
[1] T
> class(x)<-"facto"
> is.numeric(x) 
[1] T
> class(x)<-"factor"
> is.numeric(x)
[1] F

...which doesn't strike me as particularly logical. I believe that we
then decided not to be bug-compatible on this issue. What are the good
reasons to behave the Splus way?

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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