data have;
infile cards truncover expandtabs;
input PatientID $ DateOfVisit D1 D2;
format DiagnosisCode: z4.0;
datalines;A 0 0881 0981
A 2 0981 0234
A 5 0234 0567
A 30 0881 .
B 0 0881 0781
B 3 0881 .
B 9 0789 0456
B 45 0781 .; data t1; set have; by PatientID ; retain x y; if first.patientid then do; x=d1;y=d2; end; if d1=x or d1=y or d2=x or d2=y; drop x y; run; proc print;run;
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