def add_frame(frame)
      raise ArgumentError, "Invalid argument 'frame'. Expected Frame, got #{frame.class}." unless frame.is_a?(Frame)
      # Do not add it again if the frame already belongs to this instance:
      @frames << frame unless @associated_frames[frame.uid]
      @associated_frames[frame.uid] = frame
    end
def add_frame(frame)
      raise ArgumentError, "Invalid argument 'frame'. Expected Frame, got #{frame.class}." unless frame.is_a?(Frame)
      # Do not add it again if the frame already belongs to this instance:
      @frames << frame unless @associated_frames[frame.uid]
      @associated_frames[frame.uid] = frame
    end
Adds a Frame to this DataSet.

 @param [Frame] frame a Frame object to be added to this data set