title: How to sort a RDD?
body: <p>I'm a beginner in Spark and Scala. This is the RDD I finally have after 3 days :</p>
  
  <pre><code>((null,18),1)
  
  ((null,17),1)
  
  ((null,16),1)
  
  ((AK,14),2)
  
  ((Lo,6),1)
  
  ((Re,7),1)
  
  ((4x,10),1)
  
  ((null,12),4)
  
  ((Re,13),1)
  
  ((Mu,19),1)
  
  ((Lo,19),2)
  
  ((null,8),1)
  
  ((null,20),3)
  </code></pre>
  
  <p>I'm supposed to sort this RDD so that all values of a kind are grouped together in ascending order. Eg:</p>
  
  <pre><code>((null,8),1)
  
  ((null,12),4)
  
  ((null,16),1)
  
  ((null,17),1)
  
  ((null,18),1)
  
  ((null,20),3)
  
  ((Lo,6),1)
  
  ((Lo,19),2)
  </code></pre>
  
  <p>I have no idea where to look or how to begin.</p>