title: How to deal with feature vector of variable length?
body: <p>Say you're trying to classify houses based on certain features:</p>
  
  <ul>
  <li>Total area </li>
  <li>Number of rooms</li>
  <li>Garage area</li>
  </ul>
  
  <p>But not all houses have garages. But when they do, their total area makes for a very discriminating feature. What's a good approach to leverage the information contained in this feature?</p>