title: ggplot2 heatmaps: using different gradients for categories
body: <p><a href="http://learnr.wordpress.com/2010/01/26/ggplot2-quick-heatmap-plotting/" rel="noreferrer">This Learning R blog post</a> shows how to make a heatmap of basketball stats using ggplot2. The finished heatmap looks like this:</p>
  
  <p><img src="https://i.stack.imgur.com/Jegil.png" alt="enter image description here"></p>
  
  <p>My question (inspired by <a href="https://learnr.wordpress.com/2010/01/26/ggplot2-quick-heatmap-plotting/#comment-450" rel="noreferrer">Jake</a> who commented on the Learning R blog post) is: would it be possible to use different gradient colors for different categories of stats (offensive, defensive, other)? </p>