code: public int rowSum(int classindex) {
      int s = 0;
      for(int i = 0; i < confusion[classindex].length; i++) {
        s += confusion[classindex][i];
      }
      return s;
    }
docs: The number of instances present in the specified row. I.e., classified as
  class <code>classindex</code>.
  
  
  @param classindex the index of the class the resulting number of instances
  has been classified as
  @return the number of instances present in the specified row