/*The PERM_GEN  macro code appears on page 103 in the
book, "SAS(R) Survival Analysis Techniques for Medical
Research, Second Edition" by Alan B. Cantor, Ph.D.  */

%macro perm_gen(indata = &syslast, time =  , cens = ,  n1 = , n2 = , group =);
%let n = %eval(&n1 + &n2);
%let ncomb = %sysfunc(comb(&n, &n1));
ods output Plan=Combinations; 
   proc plan ;
      factors replicate= &ncomb ordered
              r= &n1 of &n comb;
   run;
   
data reps; set combinations; keep replicate  i &group ;
array r{*} r1 - r&n1;
array grp{*} group1 - group&n;
do i = 1 to &n; 
grp{i} = 2;
do j = 1 to &n1;
if r{j} = i then grp{i} = 1;
end;
&group = grp{i};
output;
end;
run;
data temp; set _null_;
%do i = 1 %to &ncomb;
data temp; set temp &indata; keep &time &cens;
%end;

data reps; merge reps temp;
data temp2; set &indata; 
replicate = 0;
data reps; set temp2 reps;

run; 
%mend;