code: func (sg *SampleGroup) AvgRate() int64 {
  	sum := uint64(0)
  	for _, s := range sg.Samples {
  		sum += uint64(s.Rate())
  	}
  	return int64(sum / uint64(len(sg.Samples)))
  }
docs: // AvgRate returns the average of all the message rates in the SampleGroup