@kfbaker0206 wrote: I care because in Dataset A there are 6K id numbers 4k of which match Dataset B. The original data sets (A and B) cannot be modified. They are received from two different areas. I want the 2K from dataset A to keep their original CODE. The 4K (that have the same IDs) from Datasets A & B needs to be changed to 'H'. Use the IN= dataset option. There are three possible sets of records.  For those INA and NOT INB you want the CODE from A.  For those in INA and INB you want CODE set to 'H'.  What do you want to happen for those that are INB and NOT INA?   You could try merging the data.   data want ; merge a(in=in1 keep=id code) b(in=in2 keep=id); by id; if in1 and in2 then code='H'; else if not in1 then do; * What do you want to happen with these ? ; end; run; If it is still not clear then post sample data for four or five ids that cover all of the possible scenarios and show what values you want to get out.   Or you could adapt the SET method I posted before to reference the B set first.  That way you can tell if the there are any records in B for this particular value of ID. data want ; set B (in=in2) A; by id; if first.id; if in2 then code='H'; run; ... View more

Show us your code.   Show us your SASLOG.   Show us the output data set. ... View more