title: Count elements in pair of tuples
body: <p>I have a list of tuple</p>
  <pre><code>[(6, 0, 16), (6, 0, 76)]
  [(6, 0, 86), (6, 0, 91)]
  [(6, 2, 96), (6, 2, 97)]
  [(6, 3, 3), (6, 3, 17)]
  [(6, 4, 2), (6, 4, 41)]
  [(10, 1, 47), (10, 1, 64)]
  [(10, 2, 21), (10, 2, 35)]
  [(10, 2, 48), (10, 2, 77)]
  [(10, 4, 75), (10, 4, 76)]
  [(15, 3, 35), (15, 3, 36)]
  [(15, 3, 45), (15, 3, 61)]
  [(15, 4, 50), (15, 4, 58)]
  </code></pre>
  <p>and would want my output to be a dictionary that counts my first element of the first tuple within a pair</p>
  <p>the output should look like this:</p>
  <pre><code>{6: 5, 10: 4, 15: 3}
  </code></pre>