title: Merge with Map-Reduce. Multiple keys in one dataset
body: <p>I have two datasets:</p>
  
  <pre><code>Dataset1:
  
  Emp1 Emp2 Salary
  
  
  
  Dataset2
  
  Emp add1 add2 add3
  </code></pre>
  
  <p>The data in the Dataset 2 consists of all the employees which exist in Emp1 or Emp2 in the dataset1. </p>
  
  <p>The resultant dataset needs have each row of Dataset1 and add1 add2 add3 variables of both the employess emp1 and emp2.</p>
  
  <pre><code>Dataset3
  
  Emp1 Emp2 add1(emp1) add2(emp1)  add3(emp1) add1(emp2) add2(emp2)  add3(emp2)
  </code></pre>
  
  <p>It is basically a merge over 2 datasets but when i try and get keys from first dataset, I can get Emp1 Emp2 in a column and can get Emp1 Emp3 in another column. How do I accomplish this using map reduce since the keys are getting confused?</p>