docs: @Override
      public DataSet copy() {
          DataSet ret = new DataSet(getFeatures().dup(), getLabels().dup());
          if (getLabelsMaskArray() != null)
              ret.setLabelsMaskArray(getLabelsMaskArray().dup());
          if (getFeaturesMaskArray() != null)
              ret.setFeaturesMaskArray(getFeaturesMaskArray().dup());
          ret.setColumnNames(getColumnNames());
          ret.setLabelNames(getLabelNames());
          return ret;
      }