title: PROC SUMMARY using multiple fields as a key
body: <p>Is there a way to replicate the behaviour below using <code>PROC SUMMARY</code> without having to create the dummy variable <code>UniqueKey</code>?</p>
  
  <pre><code>DATA table1;
  input record_desc $ record_id $ response;
  informat record_desc $4. record_id $1. response best32.;
  format record_desc $4. record_id $1. response best32.;
  DATALINES;
    A001 1 300
    A001 1 150
    A002 1 200
    A003 1 150
    A003 1 99
    A003 2 250
    A003 2 450
    A003 2 250
    A004 1 900
    A005 1 100
  ;
  RUN;
  
  DATA table2;
    SET table1;
    UniqueKey = record_desc || record_id;
  RUN;
  
  PROC SUMMARY data = table2 NWAY MISSING;
    class UniqueKey record_desc record_id;
    var response;
    output out=table3(drop = _FREQ_ _TYPE_) sum=;
  RUN;
  </code></pre>