how to clear the lines in rqt_plot [closed]

edit

how to clear the lines in rqt_plot? The clear button removes the lines, but also the topics. I'd like to be able to clear the lines, but keep my topic list the same.

Scenario: I am using rqt_bag to play back some data from a bag file. I'm plotting one data from one topic, then I realize I need to compare it to another data from another topic, so I add that second one, and restart the playback.

I'm tempted to write a script to extract fields from topics and dump them to a csv file then use another tool (Libreoffice Calc or gnuplot to plot it...)