Example #1
0
 /// <summary>
 /// Information gain for an attribute on a set of examples
 /// </summary>
 private static double Importance(ICollection<Example> examples, DataAttribute attr)
 {
     return Entropy(examples) - Remainder(examples, attr);
 }
Example #2
0
        /// <summary>
        /// Remaining entropy after attribute divides example set
        /// </summary>
        private static double Remainder(ICollection<Example> examples, DataAttribute attr)
        {
            var subsets = examples.ToLookup(x => x.Attributes[attr.ColNum]);

            return subsets.Select(x => x.ToList())
                          .Select(subset => new
                              {
                                  prob = (double)subset.Count / examples.Count,
                                  entropy = Entropy(subset),
                              })
                          .Sum(x => x.prob * x.entropy);
        }