CODEWITHSUNDEEP
matlabplotoctave
s5s
s5s

Reputation: 12134

Matlab change a single point in a plot without replotting

So I have a plot of N points in the 2D plane (N can be very large). I am writing a script that is to show the workings of an algorithm. So I have for loops. At each step in the for loop I'd like to change the color of the current point (actually probably make a stem plot with just this point).

However, at the end of the step I'd like to remove the coloring of the current point so that I can color the next one. Currently I have to redraw the whole plot (incl. the 2D points). I'm not sure whether Matlab detects such things in the plotting commands but is there a way to do this without redrawing the whole plot?

For example:

plot(x,y, '*');


for j = 1:N-1
    for i = j:N
        hold on;
        %Do stuff

        plot(x,y, '*');
        hold on;
        stem(x(1), y(1), 'g*');
    end

end

Upvotes: 2

Views: 4571

Answers (2)

Amro
Amro

Reputation: 124563

A quick example:

%# plot some data
x = 1:100;
y = cumsum(rand(size(x))-0.5);
plot(x,y,'*-')

%# animate by going through each point
hold on
h = stem(x(1),y(1),'g');
hold off
for i=1:numel(x)
    %# update the stem x/y data
    set(h, 'XData',x(i), 'YData',y(i));

    %# slow down a bit, drawnow was too fast!
    pause(.1)
end

screenshot

Upvotes: 7

tmpearce
tmpearce

Reputation: 12693

Take a look at the documentation of handle graphics objects.

I'd recommend plotting the whole set of points as one object. Then, for each iteration, plot the point of interest. Save a handle to it (as in, h = plot(...);). When you're ready for the next iteration, delete the object using that handle (delete(h)), and create the next one in the same manner.

%# outside the for loop (do this once)
plot(x,y,'*');

for...
    h = stem(x(i),y(i),'g*');
    ...
    %# next iteration... i has been incremented
    delete(h);
    h = stem(x(i),y(i),'g*');
end

Upvotes: 2

Related Questions