Hello Arthur, Thanks for your help. I'm now testing the code and it has following error message I could not figure out. Can you please help? data need (drop=_:); 65 do until (last.gvkey); 66 set gooddata; 67 by gvkey; 68 array before_months(686); 69 retain months:; 70 if first.gvkey then do; 71 call missing(of before_months(*)); 72 end; 73 _month=intck('month', '01dec1969'd, DATADATE); 74 _low=max(_month-36+1,1); 75 do _j=_low to _month + span.-1; ----- 22 201 ERROR 22-322: Syntax error, expecting one of the following: a name, a quoted string, a numeric constant, a datetime constant, a missing value, arrayname, (, +, -, INPUT, NOT, PUT, ^, _NEW_, ~. ERROR 201-322: The option is not recognized and will be ignored. 76 if _month le _j then before_months(_j)=sum(before_months(_j),1); 77 end; 78 end; 79 do until (last.gvkey); 80 set gooddata; 81 by gvkey; 82 output; 83 end; 84 run;
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