How to flip through a bunch of graphs

Hi,

So I am plotting waveforms that are generated 10 times per second. Each waveform is 500 points. Waveforms are generated throughout the day so I am getting a lot of data at one time (5,000 points per second times 96,000 seconds in a day). I need a way to go through all of these waveforms quickly but not take up too much memory.

My idea is to plot a waveform, erase the waveform, plot the next waveform, erase it, plot the next, erase it etc etc. Almost like flipping through the pages of a phonebook or one of those flip books that have a picture of someone kicking a soccer ball as you flip through it. BUT I am also open to any other ideas on how to shift through large amounts of data. Are there any functions I could use for this? Any help would be appreciated

Thank you

[Walter Roberson]

This follows on from https://www.mathworks.com/matlabcentral/answers/345043-parsing-a-lot-of-data-and-then-plotting-it-dopamine-in-rat-brains which includes some sample data.

[Patrick Lydon]

Thanks Walter... Although somewhat related, and it is using the same format of data, it is not the same. I have solved my problem though using the pause function and the clf('reset') function. Now its like a stop motion picture!

[Walter Roberson]

clf('reset') is not nearly as efficient as what I describe, and you were specifically concerned with efficiency.

[Patrick Lydon]

I'm sorry Walter but I am unsure of what you described. Where is your comment?

[Patrick Lydon]

Oh excuse me, I see it now

Answer 1

[Walter Roberson]

"My idea is to plot a waveform, erase the waveform, plot the next waveform, erase it, plot the next, erase it etc etc."

Create a plot with appropriate titles and so on, and

h = plot(nan, nan, appropriate_linestyle_etc_here);

Now, for each iteration, instead of erasing the previous waveform, set() the XData and YData parameters of h to the updated values. You could hook that into a timer, or you could hook that into a WindowKeyPressFcn, or you could arrange Forward and Back push buttons, or you could hook it into a slider callback.

You could even hook it into a Pan ActionPostCallback: you would fetch the new zoom limits from the event, pull out the appropriate data range and set the XData and YData properties.

[Patrick Lydon]

I really like this idea to use forward and back push buttons, and have been trying to implement it but I am having trouble, could you be of assistance?

    tt=1;
gg=NDataPoints;
plot(x(1,tt:gg),y1(1,tt:gg),'k');
while true
   key_read = read_a_key();
   if strcmp(key_read, 'right');
     tt=tt+NDataPoints;
     gg=gg+NDataPoints;
     plot(x(1,tt:gg),y1(1,tt:gg),'k');
   elseif strcmp(key_read, 'left')
     if tt~=1;
        tt=tt-NDataPoints;
        gg=gg-NDataPoints;
        plot(x(1,tt:gg),y1(1,tt:gg),'k'); 
     else
     end
   end
end

So I have an array of ALL the waveform points both x and y values. and this simply goes waveform by waveform with NDataPoints being the number of points in the waveform. That portion is working when I just use a pause and clf('reset') commands to automatically shift through all the graphs. But I am definitely not using the WindowKeyPressFcn correctly.

Any assistance is much appreciated.

[Walter Roberson]

https://www.mathworks.com/matlabcentral/fileexchange/7465-getkey or https://www.mathworks.com/matlabcentral/fileexchange/8297-getkeywait

[Patrick Lydon]

I tried implementing your idea but I can't seem to find the bug in my code. Do you see what the problem may be?

   tt=1;
gg=NDataPoints;
h=plot(x(1,tt:gg),y1(1,tt:gg),'k');
uicontrol('Style', 'slider',...
        'Min',1,'Max',NDataPoints,'Value',1,...
        'Position', [400 20 120 20],...
        'Callback', {@src,hax});
function src(source,event)
    val = get(source, 'Value');
    set(f,'XData',XData(1,(NDataPoints*val)-(NDataPoints-1):NDataPoints*val);

[Walter Roberson]

What is hax, and why are you passing it to the callback, and why do you not have position to receive it in the parameters?

Your XData and NDataPoints are not defined in the callback function -- not unless you convert to a nested function with shared variables.

You are not updating YData as you update XData

You permit the slider value to be as large as NDataPoints, and you then multiply the fetched value by NDataPoints, so you could end up with an index as large as NDataPoints^2. That might be too much -- or it might not be enough.

function set_up_slider(x, y1, NDataPoints)
  lenx = length(x);
  gg = min(lenx, NDataPoints);
  h = plot( x(1:gg), y(1, gg), 'k');
  if lenx > NDataPoints
     uicontrol('Style', 'slider', 'Min', 1, 'Max', lenx, ...
               'Value', 1, 'Position', [400 20 120 20], ...
               'Callback', @react_to_slider);
  end

    function react_to_slider(source, event)   %nested !!
      val = round(get(source, 'Value'));
      if val + NDataPoints > lenx
         val = lenx - NDataPoints - 1;
      end
      set(source, 'Value', val);
      gg = val + NDataPoints - 1;
      set(h, 'XData', x(val : gg), 'YData', y1(val : gg));
    end
  end

[Patrick Lydon]

Thank you Walter for all of your help