%FOR variable in &LIST

I often want to provide a list of variables, say, to a macro and have it run for each of them, instead of cluttering up my code with several invocations of the same macro for each of the variables.

Suppose I want to run the macro $\%calculate\_means$ for three variables, $ret$, $retx$ and $shrout$. I could say:

  %calculate_means(ret);
  %calculate_means(retx);
  %calculate_means(shrout);

Or I could write a foreach macro:

  %macro foreach(listofvariables);

  %let i=1;
  %do %while(%scan(&listofvariables, &i, ' ')>0);
        %let thevar=%scan(&listofvariables, &i, ' ');
  
        %put We have the variable &thevar;

        %calculate_means(&thevar);

        %let i=%eval(&i+1);
        %end;
    %mend;

And call it with

%foreach(ret retx shrout);