Form 3 is a special form of ROLLUP where the second parameter passed to the transform is a GROUP and the first parameter is the first record in that GROUP. It processes through all groups in the recordset, producing one result record for each group. Aggregate functions can be used inside the transform (such as TOPN or CHOOSEN) on the second parameter. The result record set is not grouped. This form is implicitly LOCAL in nature, due to the grouping.

Example:

inrec := RECORD
  UNSIGNED6 did;
END;

outrec := RECORD(inrec)
  STRING20 name;
  UNSIGNED score;
END;

nameRec := RECORD
  STRING20 name;
END;

finalRec := RECORD(inrec)
  DATASET(nameRec) names;
  STRING20 secondName;
END;

ds := DATASET([1,2,3,4,5,6], inrec);

dsg := GROUP(ds, ROW);

i1 := DATASET([ {1, 'Kevin', 10},
                {2, 'Richard', 5},
                {5,'Nigel', 2},
                {0, '', 0}], outrec);

i2 := DATASET([ {1, 'Kevin Halligan', 12},
                {2, 'Richard Charles', 15},
                {3, 'Blake Smith', 20},
                {5,'Nigel Hicks', 100},
                {0, '', 0}], outrec);

i3 := DATASET([ {1, 'Halligan', 8},
                {2, 'Richard', 8},
                {6, 'Pete', 4},
                {6, 'Peter', 8},
                {6, 'Petie', 1},
                {0, '', 0}], outrec);
j1 := JOIN( dsg,
            i1,
            LEFT.did = RIGHT.did,
            TRANSFORM(outrec, SELF := LEFT; SELF := RIGHT),
            LEFT OUTER, MANY LOOKUP);
j2 := JOIN( dsg,
            i2,
            LEFT.did = RIGHT.did,
            TRANSFORM(outrec, SELF := LEFT; SELF := RIGHT),
            LEFT OUTER,
            MANY LOOKUP);

j3 := JOIN( dsg,
            i3,
            LEFT.did = RIGHT.did,
            TRANSFORM(outrec, SELF := LEFT; SELF := RIGHT),
            LEFT OUTER,
            MANY LOOKUP);

combined := REGROUP(j1, j2, j3);

finalRec doRollup(outRec l, DATASET(outRec) allRows) :=
          TRANSFORM
  SELF.did := l.did;
  SELF.names := PROJECT(allRows(score != 0),
                        TRANSFORM(nameRec, SELF := LEFT));
  SELF.secondName := allRows(score != 0)[2].name;
END;

results := ROLLUP(combined, GROUP, doRollup(LEFT,ROWS(LEFT)));

See Also: TRANSFORM Structure, RECORD Structure, DEDUP, EXCEPT, GROUP