[R] An index of all possible combinations of variables in a datafram e

[Dimitris Rizopoulos]

Hi Alan,

you could also try the following function which has been submitted to 
s-news some time ago:

powerSet <- function(x){
 if(length(x)==0) return(vector(mode(x), 0))
 x <- sort(unique(x))
 K <- NULL
 for(m in x) K <- rbind(cbind(K, FALSE), cbind(K, TRUE))
 out <- apply(K, 1, function(x, s) s[x], s=x)[-1]
 names(out) <- NULL
 return(out)
}

powerSet(1:5)

I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/396887
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat/
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Alan Simpson" <alan.simpson at robertsresearch.com.au>
To: <r-help at stat.math.ethz.ch>
Sent: Tuesday, September 28, 2004 6:51 AM
Subject: [R] An index of all possible combinations of variables in a 
datafram e


> Hello list
>
> Does anybody know of any way to create an index of all the possible
> combinations of variables (factors) in a data frame? ie for 3 
> factors A, B &
> C we have
>
> A
> B
> C
> AB
> AC
> BC
> ABC
>
> which equates to columns 1, 2, 3, 1:2, (1,3), 2:3 and 1:3.
>
> I realise that a function like model.matrix does this, but how to 
> get the
> seqence of the index?
>
> Any help would be greatly appreciated.
>
> Regards
>
> Alan Simpson
> Roberts Research Group
>
>
> [[alternative HTML version deleted]]
>
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