title: NSFetchRequest: Query for distinct values and count other properties values
body: <p>I try to set up an <code>NSFetchRequest</code> for an entity <code>Location</code> with properties like <code>country</code>and <code>city</code>:</p>
  
  <pre><code>country  | city
  ————————————————
  Germany  | Berlin
  USA      | San Francisco
  USA      | New York
  Germany  | Munich
  Germany  | Munich
  USA      | San Francisco
  Germany  | Stuttgart
  </code></pre>
  
  <p>The <code>NSFetchRequest</code> should return the country (or a Location object with the appropriate country) and the number of cities.</p>
  
  <pre><code>[
      { country: 'Germany', cityCount: 3 },
      { country: 'USA', cityCount: 2 }
  ]
  </code></pre>
  
  <p>I know that I can just fetch all entries and 'count it myself' but I am interested in how to set up an appropriate fetch request (or if it's possible to do so) and would like to see how you would do it! :)</p>