What does group do in the following two examples from http://pig.apache.org/docs/r0.7.0/piglatin_ref2.html#FOREACH:
Example: Nested Projection
In this example if one of the fields in the input relation is a tuple, bag or map, we can perform a projection on that field (using a deference operator).
X = FOREACH C GENERATE group, B.b2;
DUMP X; (1,{(3)}) (4,{(6),(9)}) (8,{(9)})
In this example multiple nested columns are retained.
X = FOREACH C GENERATE group, A.(a1, a2);
DUMP X; (1,{(1,2)}) (4,{(4,2),(4,3)}) (8,{(8,3),(8,4)})
Is there any difference between using group and using GROUP?
Examples:
Example: Flattening
In this example the FLATTEN operator is used to eliminate nesting.
X = FOREACH C GENERATE group, FLATTEN(A);
DUMP X; (1,1,2,3) (4,4,2,1) (4,4,3,3) (8,8,3,4) (8,8,4,3)
Another FLATTEN example.
X = FOREACH C GENERATE GROUP, FLATTEN(A.a3);
DUMP X; (1,3) (4,1) (4,3) (8,4) (8,3)
