A data step is easier, use retain to hold the multiplier and make sure to set the value when code=0. Then drop the multiplier column at the end, I've left it in for display purposes. This assumes your data is sorted as above. data want; set have; by unitid year; retain multiplier; if code=0 then multiplier=f_6; f_7=f_5*multiplier; *drop mulitplier; run; ... View more

Like Tom said, sql will be a lot easier in this case and, in fact, can do everything in just a couple of lines.  Here is the sql code and yet another way to do it in a datastep: proc sql;   create table want as     select *,a_2/sum(a_2) as f_5       from have         group by unitid,year           order by year,unitid,code   ; quit; /*or*/ proc sort data=have;   by unitid year code; run; data want (drop=sum_f_5);   do until (last.year);     set have (where=(code ne 0));     by unitid year;     sum_f_5=ifn(first.year,a_2,sum(sum_f_5,a_2));   end;   do until (last.year);     set have;     by unitid year;     f_5=a_2/sum_f_5;     output;   end; run; proc sort data=want;   by year unitid code; run; ... View more

You are using the wrong syntax.  You will need to create and ARRAY using a SAS Variable List then you can iterate through the elements in the array and use an IF statement to change the values as you see fit. ... View more