code: func (f *Field) RowTime(rowID uint64, time time.Time, quantum string) (*Row, error) {
  	if !TimeQuantum(quantum).Valid() {
  		return nil, ErrInvalidTimeQuantum
  	}
  	viewname := viewsByTime(viewStandard, time, TimeQuantum(quantum[len(quantum)-1:]))[0]
  	view := f.view(viewname)
  	if view == nil {
  		return nil, errors.Errorf("view with quantum %v not found.", quantum)
  	}
  	return view.row(rowID), nil
  }
docs: // RowTime gets the row at the particular time with the granularity specified by
  // the quantum.