code: func (m *trafficMap) insert(ip, id string, val float64) {
  	if _, ok := (*m)[ip]; !ok {
  		(*m)[ip] = make(map[string]float64)
  	}
  	(*m)[ip][id] = val
  }
docs: // insert inserts a new value to the traffic map. Overwrites
  // the value at the given ip and id if that already exists.