title: Subtracting two bags/relations in Pig
body: <p>I have two identical bags or relations (have same fields), say B1 and B2. I want to subtract B2 from B1 so that I get all those tuples that are in B1 but not in B2. The SUBTRACT function in Pig subtracts fields but I am looking for tuple subtraction like the 'difference' or 'minus' operators in SQL.</p>
  
  <p>Example: Bag/Relation R1 has following tuples</p>
  
  <pre><code>(a1, b1)
  (a2, b2)
  (a3, b3)
  (a4, b4)
  </code></pre>
  
  <p>Relation R2 has following tuples</p>
  
  <pre><code>(a1, b1)
  (a2, b2, d2)
  (a3, b3, d3)
  (a4, b4)
  </code></pre>
  
  <p>I would like to obtain the following Relation/Bag containing:</p>
  
  <pre><code>(a1, b1)
  (a4, b4)
  </code></pre>