RANCOMB Function :: SAS/IML(R) 13.1 User's Guide

RANCOMB Function

RANCOMB (n, k <, numcomb> ) ;

RANCOMB (set, k <, numcomb> ) ;

The RANCOMB function generates random combinations of k elements taken from a set of $n$ elements. The random number seed is set by the RANDSEED subroutine.

The first argument, set, can be a scalar or a vector. If set is a scalar, the function returns indices in the range 1– $n$ . If set is a vector, the number of elements of the vector determines $n$ and the RANCOMB function returns elements of set.

By default, the RANCOMB function returns a single random combination with one row and $k$ columns. If the numcomb argument is specified, the function returns a matrix with numcomb rows and k columns. Each row of the returned matrix represents a single combination.

The following statements generate five random combinations of two elements from the set $\{ 1, 2, 3, 4\}$ :

n = 4;
k = 2;
call randseed(1234);
c = rancomb(n, k, 5);
print c;

Figure 24.294: Random Pairwise Combinations of Four Items

c
1	4
1	2
2	4
2	3
1	3

The function can return combinations for arbitrary numerical or character matrices. For example, the following statements generate five random pairwise combinations of four elements:

d = rancomb({A B C D}, 2, 5);
print d;

Figure 24.295: Random Pairwise Combinations of Four Characters

d
A	D
A	B
A	D
B	D
A	B