title: How to handle new data for recommendation system?
body: <p>Here's a theoretical question. Let's assume that I have implemented two types of collaborative filtering: user-based CF and item-based CF (in the form of <a href="http://en.wikipedia.org/wiki/Slope_One" rel="nofollow">Slope One</a>).</p>
  
  <p>I have a nice data set for these algorithms to run on. But then I want to do two things:</p>
  
  <ol>
  <li>I'd like to add a new rating to the data set.</li>
  <li>I'd like to edit an existing rating.</li>
  </ol>
  
  <p>How should my algorithms handle these changes (without doing a lot of unnecessary work)? Can anyone help me with that?</p>