title: Sort NSArray according to NSDictionary
body: <p>Let's say if I have an NSArray of NSObjects:</p>
  
  <pre><code>{
    person: {
      'id':'A',
      'firstName':'Bob'
    }
    person: {
      'id':'B',
      'firstName':'Chris'
    }
    person: {
      'id':'C',
      'firstName':'Sarah'
    }
  }
  </code></pre>
  
  <p>and an NSDictionary of key-values (NSDates)</p>
  
  <pre><code>{
    'A':'13:45:12 Tuesday',
    'B':'01:45:12 Monday',
    'C':'05:45:12 Friday'
  }
  </code></pre>
  
  <p>and I want to sort the nsarray according to the the nsdictionary according to date (in this case, the order should be [personB, personA, personC]), what would be a good way to do this?</p>