code: func (h *NumericHistogram) Mean() float64 {
  	if h.total == 0 {
  		return 0
  	}
  
  	sum := 0.0
  
  	for i := range h.bins {
  		sum += h.bins[i].value * h.bins[i].count
  	}
  
  	return sum / float64(h.total)
  }
docs: // Mean returns the sample mean of the distribution