title: Python tuple list
body: <p>Can You help me to convert Python list:</p>
  
  <pre><code>[(1, 'a'), (2, 'b'), (2, 'c'), (3, 'd'), (3, 'e')]
  </code></pre>
  
  <p>so that:
  <code>(1, 'a')</code> is index 0</p>
  
  <p><code>(2, 'b'), (2, 'c')</code> are both index 1</p>
  
  <p><code>(3, 'd'), (3, 'e')</code> are both index 2</p>
  
  <p>Simply, all tuples which element[0] is equal, have same index.</p>
  
  <p>Thank You, </p>