title: Preventing duplicate NSArrays (one sorted, one unsorted)
body: <p>I have an NSArray of objects, it is unordered. It's updated from the internet so I can't order it once and guarantee it's order later. </p>
  
  <p>Each item corresponds to a table view cell, but the user can reorder these, and there are 2 sections in the tableview, although to begin with all the cells are in one section.</p>
  
  <p>So I could create a duplicate NSArray and have this ordered. And save it to the hard drive.
  But this seems quite a waste, and what do I do when a new object is added to/removed from the unordered NSArray by an update over the internet.</p>
  
  <p>So in sum:</p>
  
  <ul>
  <li><p>How do i have one unordered NSArray and one ordered without duplication (and waste of memory)?</p></li>
  <li><p>And how do I deal with updates to the unordered array, when the user hasn't set a location for new objects/cells?</p></li>
  </ul>