Basic syntax:
---------------                                         
combin x, k(#)                                          
                                                
Description     
-----------                                     
combin generates `k' unique combinations from a set of `n' objects, where `k' i
> s not greater than 5 (2 =< k <= 5).
Program first arranges `k' possible permutations and then retains unique combin
> ations. It supports both string and numeric variables.
                                                
combination: [n! / k!(n-k)!]                    

n: total number of observations                         
k: unique combinations                          
                                                
                                                
(original)            k unique combinations (k=2, n=4)                  
  +----+              +-----+-----+
  | x  |    ===>      | x_1 | x_2 |
  +----+              +-----+-----+
  | A  |              |  A  |  B  |
  | B  |              |  A  |  C  |
  | C  |              |  A  |  D  |
  | D  |              |  B  |  C  |
  +----+              |  B  |  D  |
                      |  C  |  D  |
                      +-----+-----+
                                                
        
        
(original)             k unique combinations (k=3, n=4) 
  +----+              +-----+-----+-----+   
  | x  |    ===>      | x_1 | x_2 | x_3 |
  +----+              +-----+-----+-----+
  | A  |              |  A  |  B  |  C  |
  | B  |              |  A  |  B  |  D  |
  | C  |              |  A  |  C  |  D  |
  | D  |              |  B  |  C  |  D  |
  +----+              +-----+-----+-----+

        
Examples:
---------
combin x, k(2)                                          
combin x, k(3)                                          
combin x, k(4)                                          
combin x, k(5)                                          
                                                

Author                                          
Muhammad Rashid Ansari                                          
INSEAD Business School                                          
1 Ayer Rajah Avenue, Singapore 138676                                          
>  
rashid.ansari@insead.edu