Nested cross
------------
Key: PIG-1916
URL: https://issues.apache.org/jira/browse/PIG-1916
Project: Pig
Issue Type: New Feature
Components: impl
Reporter: Daniel Dai
Fix For: 0.10
It is useful to have cross inside foreach nested statement. One typical for
nested foreach is after cogroup two relations, we want to flatten the records
of the same key, and do some processing. This is naturally to be achieved by
cross. Eg:
{code}
C = cogroup user by uid, session by uid;
D = foreach C {
crossed = cross user, session; -- To flatten two input bags
filtered = filter crossed by user::region == session::region;
result = foreach crossed generate processSession(user::age, user::gender,
session::ip); --Nested foreach Jira: PIG-1631
generate result;
}
{code}
If we don't have cross, user have to write a UDF process the bag user, session.
It is much harder than a UDF process flattened tuples. This is especially true
when we have nested foreach statement(PIG-1631).
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