code: func (t *Collector) Count(name string, value int64, rate float64, tags ...string) {
  	t.lock.Lock()
  	t.changed = true
  	defer t.lock.Unlock()
  
  	idx, ok := t.indexes[name]
  	if !ok {
  		idx = len(t.stats)
  		t.stats = append(t.stats, 0)
  		t.names = append(t.names, name)
  		t.indexes[name] = idx
  	}
  	if rate < 1 {
  		if rand.Float64() > rate {
  			return
  		}
  	}
  	t.stats[idx] += value
  }
docs: // Count adds value to the named stat at the specified rate.