code: func (s *StreamStats) Combine(o *StreamStats) {
  	count := s.Count + o.Count
  
  	// Compute combined online variance statistics
  	delta := o.mean - s.mean
  	mean := s.mean + delta*float64(o.Count)/float64(count)
  	vM2 := s.vM2 + o.vM2 + delta*delta*float64(s.Count)*float64(o.Count)/float64(count)
  
  	s.Count = count
  	s.Total += o.Total
  	if o.Min < s.Min {
  		s.Min = o.Min
  	}
  	if o.Max > s.Max {
  		s.Max = o.Max
  	}
  	s.mean = mean
  	s.meanOfSquares += (o.meanOfSquares - s.meanOfSquares) * float64(o.Count) / float64(count)
  	s.vM2 = vM2
  }
docs: // Combine updates s's statistics as if all samples added to o were
  // added to s.