title: hadoop pig bag subtraction
body: <p>I'm using Pig to parse my application logs to know which exposed methods have been called by a user that wasn't called the last month (by the same user).</p>
  
  <p>I have managed to get methods called grouped by users before last month and after last month :</p>
  
  <p>BEFORE last month relation sample</p>
  
  <pre><code>u1      {(m1),(m2)}
  u2      {(m3),(m4)}
  </code></pre>
  
  <p>AFTER last month relation sample</p>
  
  <pre><code>u1      {(m1),(m3)}
  u2      {(m1),(m4)}
  </code></pre>
  
  <p>What I want is to find, by users, which methods are in AFTER that are not in BEFORE, that is </p>
  
  <p>NEWLY_CALLED expected result</p>
  
  <pre><code>u1      {(m3)}
  u2      {(m1)}
  </code></pre>
  
  <p>Question : how can I do that in Pig ? is it possible to subtract bags ?</p>
  
  <p>I have tried DIFF function but it does not perform the expected subtraction.</p>
  
  <p>Regards,</p>
  
  <p>Joel</p>