# Re: [R] give all combinations

From: Robin Hankin <rksh1_at_cam.ac.uk>
Date: Mon, 01 Sep 2008 09:36:04 +0100

Hi Yuan, Lucien, List.

try this:

f <-
function (...)
{

args <- list(...)
if(length(args)==0){

return(NULL)
}
if (length(args) == 1) {

return(args[])
}
if (length(args) > 2) {

```        jj <- do.call("Recall", c(args[-1]))
return(do.call("Recall", c(list(args[]), list(jj) )))
```
}
a <- args[]
b <- args[]
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].

HTH rksh

Lucien Lemmens wrote:
>
>
> 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
>  "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
>  "aaa" "aab" "aac" "aba" "abb" "abc" "acb" "acc" "bbb" "bbc" "bcc" "ccc"
>
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