code: public Histogram getResidualPlotAllClasses() {
          String title = "Residual Plot - All Predictions and Classes";
          int[] counts = residualPlotOverall.data().asInt();
          return new Histogram(title, 0.0, 1.0, counts);
      }
docs: Get the residual plot for all classes combined. The residual plot is defined as a histogram of<br>
  |label_i - prob(class_i | input)| for all classes i and examples.<br>
  In general, small residuals indicate a superior classifier to large residuals.
  
  @return Residual plot (histogram) - all predictions/classes