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| Functions and CALL Routines |
CALL ALLPERM Routine
Generates all permutations of the values of several variables in a minimal change order.
| Category: | Combinatorial |
Syntax |
| CALL ALLPERM(count, variable-1<, variable-2 ...>); |
Arguments
- count
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specifies an integer variable that ranges from 1 to the number of permutations.
- variable
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specifies either 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 |
CALL ALLPERM Processing
Use the CALL ALLPERM routine in a loop where the first argument to CALL ALLPERM takes each integral value from 1 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 consecutive variables are interchanged.
Note: You can compute the number of permutations by
using the PERM function. See PERM Function for more information. ![[cautionend]](../../../../common/63294/HTML/default/images/cautend.gif)
If you call the 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, your result will not be the Kth permutation (except when K is 1). To get the Kth permutation, you must call the ALLPERM routine K times, with the first argument taking values from 1 through K in that exact order.
ALLPERM always produces N! permutations even if some of the variables have equal values or missing values. If you want to generate only the distinct permutations when there are equal values, or if you want to omit missing values from the permutations, use the LEXPERM function instead.
Using the CALL ALLPERM Routine with Macros
You can call the ALLPERM routine when you use the %SYSCALL macro. In this case, the variable arguments are not required to be the same type or length. If %SYSCALL identifies an argument as numeric, then %SYSCALL reformats the returned value.
If an error occurs during the execution of the CALL ALLPERM routine, then both of the following values are set:
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&SYSERR is assigned a value that is greater than 4.
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&SYSINFO is assigned a value that is less than -100.
If there are no errors, then &SYSERR is set to zero, and &SYSINFO is set to one of the following values:
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0 if count=1
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J if 1<count<=N! and the values of variable-J and variable-K were interchanged, where J+1=K
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-1 if count>N!
| Comparisons |
SAS provides three functions or CALL routines for generating all permutations:
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ALLPERM generates all possible permutations of the values, missing or nonmissing, of several variables. Each permutation is formed from the previous permutation by interchanging two consecutive values.
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LEXPERM generates all distinct permutations of the nonmissing values of several variables. The permutations are generated in lexicographic order.
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LEXPERK generates all distinct permutations of K of the nonmissing values of N variables. The permutations are generated in lexicographic order.
ALLPERM is the fastest of these functions and CALL routines. LEXPERK is the slowest.
| Examples |
Example 1: Using CALL ALLPERM in a DATA Step
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;
SAS writes the following output to the 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
Example 2: Using CALL ALLPERM with Macros
The following is an example of the CALL ALLPERM routine that is used with macros. The output includes values for the %SYSINFO macro.
%macro test; %let x1=ant; %let x2=-.1234; %let x3=1e10; %let x4=hippopotamus; %let nperm=%sysfunc(perm(4)); %do j=1 %to &nperm+1; %syscall allperm(j, x1, x2, x3, x4); %let jfmt=%qsysfunc(putn(&j,5.)); %put &jfmt: &x1 &x2 &x3 &x4 sysinfo=&sysinfo; %end; %mend; %test;
SAS writes the following output to the log:
1: ant -0.1234 10000000000 hippopotamus sysinfo=0 2: ant -0.1234 hippopotamus 10000000000 sysinfo=3 3: ant hippopotamus -0.1234 10000000000 sysinfo=2 4: hippopotamus ant -0.1234 10000000000 sysinfo=1 5: hippopotamus ant 10000000000 -0.1234 sysinfo=3 6: ant hippopotamus 10000000000 -0.1234 sysinfo=1 7: ant 10000000000 hippopotamus -0.1234 sysinfo=2 8: ant 10000000000 -0.1234 hippopotamus sysinfo=3 9: 10000000000 ant -0.1234 hippopotamus sysinfo=1 10: 10000000000 ant hippopotamus -0.1234 sysinfo=3 11: 10000000000 hippopotamus ant -0.1234 sysinfo=2 12: hippopotamus 10000000000 ant -0.1234 sysinfo=1 13: hippopotamus 10000000000 -0.1234 ant sysinfo=3 14: 10000000000 hippopotamus -0.1234 ant sysinfo=1 15: 10000000000 -0.1234 hippopotamus ant sysinfo=2 16: 10000000000 -0.1234 ant hippopotamus sysinfo=3 17: -0.1234 10000000000 ant hippopotamus sysinfo=1 18: -0.1234 10000000000 hippopotamus ant sysinfo=3 19: -0.1234 hippopotamus 10000000000 ant sysinfo=2 20: hippopotamus -0.1234 10000000000 ant sysinfo=1 21: hippopotamus -0.1234 ant 10000000000 sysinfo=3 22: -0.1234 hippopotamus ant 10000000000 sysinfo=1 23: -0.1234 ant hippopotamus 10000000000 sysinfo=2 24: -0.1234 ant 10000000000 hippopotamus sysinfo=3 25: -0.1234 ant 10000000000 hippopotamus sysinfo=-1
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Copyright © 2011 by SAS Institute Inc., Cary, NC, USA. All rights reserved.