title: count distinct values in spreadsheet
body: <p>I have a Google spreadsheet with a column that looks like this:</p>
  
  <pre><code>City
  ----
  London
  Paris
  London
  Berlin
  Rome
  Paris
  </code></pre>
  
  <p>I want to count the appearances of each distinct city (so I need the city name and the number of appearances).</p>
  
  <pre><code>City   | Count
  -------+------
  London |  2
  Paris  |  2
  Berlin |  1
  Rome   |  1
  </code></pre>
  
  <p>How do I do that?</p>