title: how to re-name alias in PIG
body: <p>I just started learning pig and I have a problem with re-naming an alias. Want I want to do is read a file, filter it, and then join it by itself. What I did is this:</p>
  
  <pre><code>register s3n://uw-cse-344-oregon.aws.amazon.com/myudfs.jar
  raw = LOAD 's3n://uw-cse-344-oregon.aws.amazon.com/cse344-test-file' USING TextLoader as (line:chararray);
  ntriples = foreach raw generate FLATTEN(myudfs.RDFSplit3(line)) as (subject:chararray,predicate:chararray,object:chararray);
  
  ntriples2 = foreach raw generate FLATTEN(myudfs.RDFSplit3(line)) as (subject2:chararray,predicate2:chararray,object2:chararray);
  X = FILTER ntriples BY (subject matches '.*business.*');
  X2 = FILTER ntriples2 BY (subject2 matches '.*business.*');
  joined= join X by subject, X2 by subject2;
  joined = DISTINCT joined;
  store joined into '/user/hadoop/join-results' using PigStorage();  
  </code></pre>
  
  <p>as you can see I read and filter the file twice in order two have two different alias for each column. How can I simply copy the filtered collection and assign it new aliases? This operation was supposed to take 18 mins, but took 1.5 hour. </p>