code: func FieldValueUnmarshaller(format Format) RecordUnmarshaller {
  	return func(text string) (pilosa.Record, error) {
  		parts := strings.Split(text, ",")
  		if len(parts) < 2 {
  			return nil, errors.New("Invalid CSV")
  		}
  		value, err := strconv.ParseInt(parts[1], 10, 64)
  		if err != nil {
  			return nil, errors.New("Invalid value")
  		}
  		switch format {
  		case ColumnID:
  			columnID, err := strconv.ParseUint(parts[0], 10, 64)
  			if err != nil {
  				return nil, errors.New("Invalid column ID at line: %d")
  			}
  			return pilosa.FieldValue{
  				ColumnID: uint64(columnID),
  				Value:    value,
  			}, nil
  		case ColumnKey:
  			return pilosa.FieldValue{
  				ColumnKey: parts[0],
  				Value:     value,
  			}, nil
  		default:
  			return nil, fmt.Errorf("Invalid format: %d", format)
  		}
  	}
  }
docs: // FieldValueUnmarshaller is a function which creates a Record from a CSV file line with value data.