code: func mergeSamples(a, b []prompb.Sample) []prompb.Sample {
  	result := make([]prompb.Sample, 0, len(a)+len(b))
  	i, j := 0, 0
  	for i < len(a) && j < len(b) {
  		if a[i].Timestamp < b[j].Timestamp {
  			result = append(result, a[i])
  			i++
  		} else if a[i].Timestamp > b[j].Timestamp {
  			result = append(result, b[j])
  			j++
  		} else {
  			result = append(result, a[i])
  			i++
  			j++
  		}
  	}
  	result = append(result, a[i:]...)
  	result = append(result, b[j:]...)
  	return result
  }
docs: // mergeSamples merges two lists of sample pairs and removes duplicate
  // timestamps. It assumes that both lists are sorted by timestamp.