Find a maximum/minimum/average of ordered sequencing obs within a group with SQL. For  maximum/average one just needs to replace min with max/mean function.


data test;
RETAIN G '  ';
input x1 $ x2;
IF G NE X1 THEN DO;
   G=X1;
   ID=0;
END;
ID+1;
datalines;
01 1
01 2
01 1
01 4
01 5
02 1
02 -3
02 3
02 4
02 5
;
PROC SQL;
  SELECT DISTINCT A.X1, A.ID ,A.X2, MIN(B.X2) AS MIN
  FROM TEST AS A
   JOIN TEST AS B
  ON
   A.X1=B.X1
  AND
  (A.ID-B.ID= 0 OR A.ID-B.ID= 1 OR A.ID-B.ID= 2)
  GROUP BY A.X1, A.ID
  ORDER BY A.X1, A.ID
;
QUIT;