title: I need a formula that returns how many times an unique value appears in a given date
body: <p>In a spreadsheet in Google Spreadsheets, I`m trying to solve this:</p>
  
  <pre><code>17/02/2012  banana
  17/02/2012  banana
  17/02/2012  banana
  17/02/2012  apple
  18/02/2012  apple
  18/02/2012  apple
  </code></pre>
  
  <p>I need a formula that returns how many times an unique value appears in a given date.</p>
  
  <p>Example: </p>
  
  <pre><code>17/02/2012 - two unique values 
  18/02/2012 - one unique value
  </code></pre>
  
  <p>Anyone can help?</p>