code: public OnLineStatistics getOnlineDenseStats()
      {
          OnLineStatistics stats = new OnLineStatistics();
          double N = getNumNumericalVars();
          for(int i = 0; i < size(); i++)
              stats.add(getDataPoint(i).getNumericalValues().nnz()/N);
          return stats;
      }
docs: Returns an {@link OnLineStatistics } object that is built by observing
  what proportion of each data point contains non zero numerical values.
  A mean of 1 indicates all values were fully dense, and a mean of 0
  indicates all values were completely sparse (all zeros).
  
  @return statistics on the percent sparseness of each data point