Set difference
Monday, March 07, 2011
2:48 PM
Set difference
Use COGROUP to determine whether sets are empty or not. 
USE FILTER to strike elements that are present in the second set: 
Example: if s1:{thing:chararray} and s2:{thing:chararray} then
grps = COGROUP s1 BY thing, s2 BY thing; 
grp2 = FILTER grps by IsEmpty(s2);
diff = FOREACH grp2 GENERATE group as thing;  