code: public static double harmonicMean(FlatDataCollection flatDataCollection) {
  	    int n = 0;
          double harmonicMean = 0.0;
          
          Iterator<Double> it = flatDataCollection.iteratorDouble();
          while(it.hasNext()) {
              Double v = it.next();
              if(v!=null) {
                  ++n;
                  harmonicMean+=1.0/v;
              }
          }
          
          harmonicMean=n/harmonicMean;
          
          return harmonicMean;
      }
docs: Calculates Harmonic Mean
  
  @param flatDataCollection
  @return