Permutes the values of the arguments, and returns a random combination of k out of n values.

Category: | Combinatorial |

is a numeric variable that contains the random number seed. For more information about seeds, see Seed Values.

is the number of values that you want to have in the random combination.

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

If there are n variables, CALL RANCOMB permutes the values
of the variables in such a way that the first k values are sorted in ascending order and form a random combination
of k out of the n values. That is, all n!/(k!(n-k)!) combinations of k out of the n values are equally likely to be returned as the first k values.

You can call the CALL
RANCOMB routine when you use the %SYSCALL macro. In this case, the variable arguments are not required to be the
same type or length. However, if the first k values that are returned include both character and numeric values,
then those values are not sorted. If %SYSCALL identifies an argument
as numeric, then %SYSCALL reformats the returned value.

The following example
shows how to generate random combinations of given values by using
the CALL RANCOMB routine.

data _null_; array x x1-x5 (1 2 3 4 5); seed = 1234567890123; do n=1 to 10; call rancomb(seed, 3, of x1-x5); put seed= @20 ' x= ' x1-x3; end; run;

Log Output from Using the CALL RANCOMB Routine in a DATA Step

seed=1332351321 x= 2 4 5 seed=829042065 x= 1 3 4 seed=767738639 x= 2 3 5 seed=1280236105 x= 2 4 5 seed=670350431 x= 1 2 5 seed=1956939964 x= 2 3 4 seed=353939815 x= 1 3 4 seed=1996660805 x= 1 2 5 seed=1835940555 x= 2 4 5 seed=910897519 x= 2 3 4

%macro test; %let x1=ant; %let x2=-.1234; %let x3=1e10; %let x4=hippopotamus; %let x5=zebra; %let k=3; %let seed = 12345; %do j=1 %to 10; %syscall rancomb(seed, k, x1, x2, x3, x4, x5); %put j=&j &x1 &x2 &x3; %end; %mend; %test;

j=1 -0.1234 hippopotamus zebra j=2 hippopotamus -0.1234 10000000000 j=3 hippopotamus ant zebra j=4 -0.1234 zebra ant j=5 -0.1234 ant hippopotamus j=6 10000000000 hippopotamus ant j=7 10000000000 hippopotamus ant j=8 ant 10000000000 -0.1234 j=9 zebra -0.1234 10000000000 j=10 zebra hippopotamus 10000000000

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