code: public static ConfusionMatrix createCumulativeMatrix(ConfusionMatrix... matrices)
      {
          ConfusionMatrix result = new ConfusionMatrix();
  
          for (ConfusionMatrix matrix : matrices) {
              for (Map.Entry<String, Map<String, Integer>> gold : matrix.map.entrySet()) {
                  for (Map.Entry<String, Integer> actual : gold.getValue().entrySet()) {
                      result.increaseValue(gold.getKey(), actual.getKey(), actual.getValue());
                  }
              }
          }
  
          return result;
      }
docs: Sums up all matrices into a new one
  
  @param matrices confusion matrices
  @return confusion matrix