* SAS code for section 3.2 -- Default Knots;
* default_knots.macro;

%macro default_knots(librefknots=,data=,knotdata=,varknots=,numknots=);  
proc sort data=&data (keep=&varknots) out=q1;
  by &varknots;
run;
data q2;
  set q1;
  by &varknots;
  if first.&varknots;
run;
data &librefknots..&knotdata;
  set q2 nobs=n;
  knotsp=int(n/5);
  if knotsp>=35 then kmx=35; else
  if knotsp<35 then kmx=knotsp; 
  %if &numknots ne  %then %do; 
    ktemp=&numknots;
    if 1 <= ktemp <= 35 then kmx=ktemp;
  %end;
  kintrvl=round(n/kmx);
  knotsok=mod(_n_,kintrvl);     
  knots=&varknots;
  if knotsok=0 or _n_=n-1 then output; *also want the obs next to last one;  
  keep knots;
run;
%mend;