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" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
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
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