title: Ordered tally of the cumulative number of unique words seen by a given position
body: <p>I have a list of words given below (example):</p>
  
  <pre><code>['the', 'counter', 'starts', 'the', 'starts', 'for']
  </code></pre>
  
  <p>I want to process this list in order and generate a <code>pair (x,y)</code> where x is incremented with each word and y is incremented only when it sees a unique word. 
  So for the given example, my output should be like:<br> <code>[(1,1) (2,2), (3,3) (4,3) (5,3) (6,4)]</code></p>
  
  <p>I am not sure about how to do this in python. It would be great if i can get some insights on how to do this.
  Thanks.</p>