Merge pull request #8 from RobinLassonde/master

Rescue error that is raised when ID3 prediction fails on a row of data

lib/ai4r/classifiers/id3.rb

@@ -280,7 +280,7 @@ def initialize(data_labels, index, values, nodes)
 
       def value(data)
         value = data[@index]
-        return rule_not_found if !@values.include?(value)
+        return ErrorNode.new.value(data) if !@values.include?(value)
         return nodes[@values.index(value)].value(data)
       end
 
@@ -313,9 +313,13 @@ def get_rules
       end
     end
 
+    class ModelFailureError < StandardError
+      default_message = "There was not enough information during training to do a proper induction for this data element."
+    end
+
     class ErrorNode #:nodoc: all
       def value(data)
-        raise "There was not enough information during training to do a proper induction for this data element."
+        raise ModelFailureError, "There was not enough information during training to do a proper induction for the data element #{data}."
       end
       def get_rules
         return []

test/classifiers/id3_test.rb

@@ -203,6 +203,18 @@ def test_rules_eval
     eval id3.get_rules
     assert_equal 'N', marketing_target
   end
+
+  def test_model_failure
+    bad_data_items = [  ['a', 'Y'],
+                        ['b', 'N'],
+            ]
+    bad_data_labels = ['bogus', 'target']
+    id3 = ID3.new.build(DataSet.new(:data_items =>bad_data_items, :data_labels => bad_data_labels))
+    assert_raise ModelFailureError do
+      id3.eval(['c'])
+    end
+    assert_equal true, true
+  end
 end