title: join 2 RDDs using scala
body: <p>I have two <code>RDDs</code></p>
  
  <p>The first one <code>(productID,category)</code></p>
  
  <p>The second one <code>(customerID,productID,quantity)</code></p>
  
  <p>How can I make output looks like <code>(customerID,category,quantity)</code>?</p>
  
  <p>The logic is to replace each <code>productID</code> of second <code>rdd</code> with corresponding <code>category</code> of first <code>rdd</code>.</p>
  
  <p>I would like to use scala for the solution</p>