[
https://issues.apache.org/jira/browse/PIG-1916?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016083#comment-13016083
]
Zhijie Shen commented on PIG-1916:
----------------------------------
I found the POCross.java in branch-0.6. Together with POCross, other classes in
"org.apache.pig.backend.local.executionengine.physicalLayer.relationalOperator"
have been removed as well in the latest version. I checked into
"MRCompiler.java", and found the "pigContext.getExecType()" is seldom checked
in the visitXXXX functions. So how does Pig distinguish between local execution
and hadoop execution? I'm a bit confused here.
> 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
--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira
