Code for Measuring Predictor Importance

• predictor_importance_utils.R (some functions for looking at predictor correlations)
  
• chap_18_prob_1.R (solves chapter 18 problem 1)
  
• chap_18_prob_2.R (solves chapter 18 problem 2)
  
• chap_18_prob_3.R (solves chapter 18 problem 3)