title: How to engineer features for machine learning
body: <p>Do you have some advices or reading how to engineer features for a machine learning task?
  Good input features are important even for a neural network. The chosen features will affect the needed number of hidden neurons and the needed number of training examples.</p>
  
  <p>The following is an example problem, but I'm interested in feature engineering in general.</p>
  
  <p><strong>A motivation example:</strong> 
  What would be a good input when looking at a puzzle (e.g., <a href="http://en.wikipedia.org/wiki/Fifteen_puzzle" rel="noreferrer">15-puzzle</a> or <a href="http://en.wikipedia.org/wiki/Sokoban" rel="noreferrer">Sokoban</a>)? Would it be possible to recognize which of two states is closer to the goal?</p>