[R] RE: [S] Different behaviour of unique(), R vs. Splus.

[Liaw, Andy]

The source of the incompatibility:

In S-PLUS 6.2:

> methods("unique")
               splus            splus          menu                 splus 
 "unique.data.frame" "unique.default" "unique.name" "unique.rowcol.names"


In R-1.9.1:

> methods("unique")
[1] unique.array      unique.data.frame unique.default    unique.matrix    


Unless there's some sort of coordination (or even just separate effort) on
either/both R Core and Insightful developers to make sure there's agreement
on what methods to provide in the base code, such problem can only get
worse, not better, I guess.

Best,
Andy


> From: Rolf Turner
> 
> Apologies for the cross-posting, but I thought this snippet of info
> might be vaguely interesting to both lists.
> 
> I did a ***brief*** search to see if this issue had previously been
> discussed and found nothing.  So I thought I'd tell the list about a
> difference in behaviour between unique() in R and unique() in Splus
> which bit me just now.
> 
> I was trying to convert a package from Splus to R and got nonsense
> answers in R.  Turned out that within the bowels of the package I was
> doing something like
> 
> 	u <- unique(y)
> 
> where y was a matrix of integer values.  In Splus this gives a
> (short) vector of unique values.  In R it gives a matrix of the same
> dimensionality as y, except that any duplicated rows are eliminated.
> 
> (This looks like being very useful --- once you know about it.  And
> it was probably mentioned in the R release notes at one time, but, as
> Dr. Hook says, ``I was stoned and I missed it.'')
> 
> E.g.
> 	set.seed(42)
> 	m <- matrix(sample(1:5,20,TRUE),5,4)
> 	u <- unique(m)
> 
> In R ``u'' is identical to ``m''; in Splus ``u'' is vector (of
> length 5).
> 
> To get what I want in R I simply need to do
> 
> 	u <- unique(as.vector(y))
> 
> Simple, once you know.  Took me a devil of a long time to track down
> what was going wrong, but!
> 
> 					cheers,
> 
> 						Rolf Turner
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