CALL ALLPERM Routine

Generates all permutations of the values of several variables

Category: Mathematical

Syntax

CALL ALLPERM ( k , variable-1 <, variable-2, ... >);

Arguments

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.

Details

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' on page 517 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 k th permutation (except when k is one). To get the k th permutation, you must call the ALLPERM routine k times, with the first argument having values from 1 through k in that exact order.

Examples

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

 data _null_;     array x [4]  ('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

CALL ALLPERM Routine