CALL ALLPERM Routine

Arguments

k

specifies an integer value that ranges from one to the number of permutations.

variable

specifies all numeric variables or all character variables that have the same length. The values of these variables are permuted.

Requirement:	Initialize these variables before you call the ALLPERM routine.
Restriction:	Specify no more than 18 variables.

Use the CALL ALLPERM routine in a loop where the first argument accepts each integral value from one to the number of permutations. On the first call, the argument types and lengths are checked for consistency. On each subsequent call, the values of two of the variables are interchanged. Because each permutation is generated from the previous permutation by a single interchange, the algorithm is very efficient.

Note:   You can compute the number of permutations by using the FACT function. See FACT Function for more information.  

If you use the CALL ALLPERM routine and the first argument is out of sequence, the results are not useful.

In particular, if you initialize the variables and then immediately call the ALLPERM routine with a first argument of k, for example, your result will not be the kth permutation (except when k is one). To get the kth permutation, you must call the ALLPERM routine k times, with the first argument having values from 1 through k in that exact order.

The following example generates permutations of given values by using the CALL ALLPERM routine.

data _null_;
   array x [4] $3 ('ant' 'bee' 'cat' 'dog'); 
   n=dim(x);
   nfact=fact(n); 
      do i=1 to nfact;   
         call allperm(i, of x[*]);
         put i 5. +2 x[*];
      end;
run;

The following lines are written to the SAS log:

    1  ant bee cat dog
    2  ant bee dog cat
    3  ant dog bee cat
    4  dog ant bee cat
    5  dog ant cat bee
    6  ant dog cat bee
    7  ant cat dog bee
    8  ant cat bee dog
    9  cat ant bee dog
   10  cat ant dog bee
   11  cat dog ant bee
   12  dog cat ant bee
   13  dog cat bee ant
   14  cat dog bee ant
   15  cat bee dog ant
   16  cat bee ant dog
   17  bee cat ant dog
   18  bee cat dog ant
   19  bee dog cat ant
   20  dog bee cat ant
   21  dog bee ant cat
   22  bee dog ant cat
   23  bee ant dog cat
   24  bee ant cat dog

Copyright © 2007 by SAS Institute Inc., Cary, NC, USA. All rights reserved.