Optimize live plotting with a large data set

Hi,

I have a large data set (16 000 datas) that I am trying do a live plots. But I notice that it getting slower as the code progress, are there anyway to optimize it and make the code faster?

function [] = live_plot(table)
    % this function will perfrom live plotting using an input array  
    graph_len = size(table); 
    figure
    
    for i = 2:graph_len(1)
        
        % graph number 1
        subplot(2,1,1)
        hold on
        plot(table(i-1:i,1),table(i-1:i,2), "b")
        plot(table(i-1:i,1),table(i-1:i,3), '--', 'Color',[1 0 0])
        hold off
        
        
        %graph number 2
        subplot(2,1,2)
        hold on
        plot(table(i-1:i,1),table(i-1:i,4), "b")
        plot(table(i-1:i,1),table(i-1:i,5), '--', 'Color',[1 0 0])
        hold off
        pause(0.00001)
    end
end

Answer 1

[Les Beckham]

You definitely don't want to call plot repeatedly inside your loop.

Here is a suggested approach where I created the plot outside the loop and then just update the data for each of the lines in the plot during the loop. Note that running this in Answers won't show the animation. It will just show the final result.

This definitely runs faster than your current code (I tried it on my desktop Matlab).

Adapt as needed.

You might also want to try the animated line function.

t = (0:1e-3:6*pi).';
data = [t sin(t) cos(t) 2*sin(t) -2*cos(t)]; % example data (18850 rows of data)

figure
% initially, just plot the first two points to initialize the plot
h = plot(data(1:2,1), data(1:2,2), data(1:2,1), data(1:2,3), data(1:2,1), data(1:2,4), data(1:2,1), data(1:2,5));
grid on
xlim([0 max(t)]) % manually set the x and y limits so Matlab won't automatically adjust while looping
ylim([1.5*min(min(data(:,2:5))) 1.5*max(max(data(:,2:5)))])
for i = 3:numel(t)
    for iLine = 1:numel(h)
        h(iLine).XData = [h(iLine).XData data(i,1)]; % add points one-by-one to the existing lines
        h(iLine).YData = [h(iLine).YData data(i,iLine+1)];
    end
    drawnow limitrate
end

[Khang Nguyen]

I have multiple plots like this I want to update at the same time! I am not sure how to include them using your method!

[Les Beckham]

You just need to keep the handles to each of the subplots and then update as I did above.

Here's an example.

t = (0:1e-3:6*pi).';
data = [t sin(t) cos(t) 2*sin(t) -2*cos(t)];

figure
num_subplots = 4;
for iPlot = 1:num_subplots % create the subplots and plot the first two points to initialize the plot
    hs = subplot(2,2,iPlot);
    h(iPlot) = plot(data(1:2,1), data(1:2,iPlot+1));
    set(hs, 'XLim', [0 max(t)])
    set(hs, 'YLim', [1.5*min(min(data(:,iPlot+1))) 1.5*max(max(data(:,iPlot+1)))])
    grid on
end

for i = 3:numel(t)
    for iLine = 1:numel(h)
        h(iLine).XData = [h(iLine).XData data(i,1)]; % add points one-by-one to the existing lines
        h(iLine).YData = [h(iLine).YData data(i,iLine+1)];
    end
    drawnow limitrate
end