Question

Sorry for the non-descriptive title but I don t know whether there s a word for what I m trying to achieve.

Let s assume that I have a list of names of different classes like

c(  1 ,  2 ,  3 ,  4 )

I d like to generate all possible permutation pairs out of this so that there are no reverse-duplicates. So what I d like to have is something like

Note that I don t have e.g. 2 1 because I already have 1 2 . Is there an easy way to achieve this in R?

Answer 1

> x<-c( 1 , 2 , 3 , 4 )
> combn(x,2)
     [,1] [,2] [,3] [,4] [,5] [,6]
[1,] "1"  "1"  "1"  "2"  "2"  "3" 
[2,] "2"  "3"  "4"  "3"  "4"  "4"