title: C# LINQ counting elements with DISTINCT
body: <p>I have a collection of KeyValuePair items with DateTime as key and a string as value.
  Basically my data looks like:</p>
  
  <pre><code>12/07/2013 - 10220
  12/07/2013 - 10220
  12/07/2013 - 12220
  12/07/2013 - 11240
  12/07/2013 - 15220
  13/07/2013 - 23220
  13/07/2013 - 35620
  14/07/2013 - 15620
  14/07/2013 - 15620
  </code></pre>
  
  <p>I would like to have a List of how many items (distinct) I've for each days. So the query would result in a:</p>
  
  <pre><code>12/07/2013 - 4
  13/07/2013 - 2
  14/07/2013 - 1
  </code></pre>