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https://issues.apache.org/jira/browse/PIG-1916?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13009669#comment-13009669
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Zhijie Shen commented on PIG-1916:
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I've just had quick glance at the code, and found the start point of this issue
could be the LogicalPlanGenerator.g, where current grammar doesn't support
accept the nested cross operator. Meanwhile, the LogicalPlanBuilder class lacks
buildNestedCrossOp function as well. Hence to add nested cross, at first,
additional codes are required in the aforementioned part of the Pig. Please
correct me if I'm wrong. Thanks! I'm going on to explore more related parts of
this issue.
> 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
> Labels: gsoc2011
> Fix For: 0.10
>
>
> It is useful to have cross inside foreach nested statement. One typical use
> case 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).
> This is a candidate project for Google summer of code 2011. More information
> about the program can be found at http://wiki.apache.org/pig/GSoc2011
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