R help - Jun 2004 - RE: [S] Different behaviour of unique(), R vs. Splus.

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
> --------------------------------------------------------------------
> This message was distributed by s-news at lists.biostat.wustl.edu.  To
> ...(s-news.. clipped)...
> 
>

On Tue, 29 Jun 2004, Liaw, Andy wrote:
> 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.
There are plans to that effect, but R moves much faster than a commercial 
product such as S-PLUS.

It seems to me a bad idea that unique (or foo) does different things for 
matrices and data frames, for as we see frequently, many users do not 
distinguish between them.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595