I need some help here.>From a vector of variable length (say, c(A,B,C,D), I need to obtain allposible combinations (order doesn't matter) of the elements. I would like a function such as: function(x,c(A,B,C,D)) to give a matrix (for x=3) like: A B C A B D A C D B C D or for x=2 A B A C A D B C B D C D And so on. Any ideas?? Thank you, Alex Ahgarin Data Management I.R.W. Co. ----------------------------------------------- FREE! The World's Best Email Address @email.com Reserve your name now at http://www.email.com -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
On Mon, 13 Dec 1999, a s wrote:> I need some help here. > >From a vector of variable length (say, c(A,B,C,D), I need to obtain all > posible combinations (order doesn't matter) of the elements. > I would like a function such as: > function(x,c(A,B,C,D)) > to give a matrix (for x=3) like: > A B C > A B D > A C D > B C D > > or for x=2 > A B > A C > A D > B C > B D > C D > > And so on. > Any ideas??There is code to do that in Venables & Ripley, called subsets. Here's a later version (from our forthcoming `S Programming' book) subsets <- function(n, r, s = 1:n) { if(mode(n) != "numeric" || length(n) != 1 || n < 1 || (n %% 1) != 0) stop("bad value of n") if(mode(r) != "numeric" || length(r) != 1 || r < 1 || (r %% 1) != 0) stop("bad value of r") if(!is.atomic(s) || length(s) < n) stop("s is either non-atomic or too short") fun <- function(n, r, s) if(r <= 0) vector(mode(s), 0) else if(r >= n) s[1:n] else rbind(cbind(s[1], Recall(n - 1, r - 1, s[-1])), Recall(n - 1, r, s[-1])) fun(n, r, s) } Use it by subs <- function(x, string) subsets(length(string), x, string) You will need quotes! Actually, this will work for any (atomic) mode of vector. If you have long strings, subs <- function(x, string) { z <- subsets(length(string), x) zz <- string[as.vector(z)] dim(zz) <- dim(z) zz } might be better. -- 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 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Alex: Bill Venables sent me these functions in response to a similar
query of mine a few months ago (you can find the full reply by searching
the R archives under the heading "avoiding loops, gaining
generality"):
subsets <- function(r, n, v = 1:n)
if(r <= 0) NULL else
if(r >= n) v[1:n] else
rbind(cbind(v[1], Recall(r - 1, n - 1, v[-1])),
Recall(r, n - 1, v[-1]))
permutations <- function(n, v = 1:n) {
if(n == 1)
return(v[1])
X <- NULL
for(i in 1:n)
X <- rbind(X,
cbind(v[i], permutations(n - 1, v[-i])))
X
}
Hope this helps.
Matt
On Mon, 13 Dec 1999, a s wrote:
> I need some help here.
> >From a vector of variable length (say, c(A,B,C,D), I need to obtain all
> posible combinations (order doesn't matter) of the elements.
> I would like a function such as:
> function(x,c(A,B,C,D))
> to give a matrix (for x=3) like:
> A B C
> A B D
> A C D
> B C D
>
> or for x=2
> A B
> A C
> A D
> B C
> B D
> C D
>
> And so on.
> Any ideas??
>
> Thank you,
> Alex Ahgarin
> Data Management
> I.R.W. Co.
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !) To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._