title: Categorical Feature
body: <p>For LibSVM.</p>
  
  <p>In 'A Practical Guide to Support Vector Classification' it is suggested that to use m number to represent an m-category attribute. For example {red, green, blue}  can be represented as (0,0,1), (0,1,0), (1,0,0).</p>
  
  <p>But in the README, it says value in the index:value pairs can only take a real number.</p>
  
  <p>Anyone knows how to represent, say (0,0,1), in the data file?</p>