give all combinations

Hi Yuan, Lucien, List.

try this:


f <-
function (...)
{
    args <- list(...)
    if(length(args)==0){
        return(NULL)
    }
    if (length(args) == 1) {
        return(args[[1]])
    }
    if (length(args) > 2) {
        jj <- do.call("Recall", c(args[-1]))
        return(do.call("Recall", c(list(args[[1]]), list(jj) )))
    }
    a <- args[[1]]
    b <- args[[2]]
    if (is.null(b)) {
        return(a)
    }
    jj <- outer(a,b,paste)
    return(jj[!lower.tri(jj)])
}



[the difficult bit (IMO) is to make f() work with any number of 
arguments; thus
f(a,a) and f(a,a,a,a,a,b,b,a,b) and whatever should also work and this 
is why
the Recall bit is needed].

Comments anyone?




HTH

rksh

 

Another solution requiring also a bit of programming is:

 l<-letters[1:3]
 c2<-c()
 for(i in 1:3){c2<-c(c2,paste(letters[i],letters[i:3],sep=""))}
 c2
[1] "aa" "ab" "ac" "bb" "bc" "cc"
 n<-length(c2)
 c3<-c();for(i in 1:n){c3<-c(c3,paste(c2[i],letters[ceiling(i/2):3],sep=""))}
 c3
 [1] "aaa" "aab" "aac" "aba" "abb" "abc" "acb" "acc" "bbb" "bbc" "bcc" "ccc"

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