Machine Learning in Java - Second Edition

The confusion matrix

Furthermore, we can inspect where a particular misclassification has been made by examining the confusion matrix. The confusion matrix shows how a specific class value was predicted:

double[][] confusionMatrix = eval_roc.confusionMatrix(); 
System.out.println(eval_roc.toMatrixString()); 

The resulting confusion matrix is as follows:

    === Confusion Matrix ===
    
      a  b  c  d  e  f  g   <-- classified as
     41  0  0  0  0  0  0 |  a = mammal
      0 20  0  0  0  0  0 |  b = bird
      0  0  3  1  0  1  0 |  c = reptile
      0  0  0 13  0  0  0 |  d = fish
      0  0  1  0  3  0  0 |  e = amphibian
      0  0  0  0  0  5  3 |  f = insect
      0  0  0  0  0  2  8 |  g = invertebrate
  

The column names in the first row correspond to the labels assigned by the classification node. Each additional row then corresponds to ...