How to detect if a plot has already existed?

What I want to do is to plot my sampling stations on a map. The map is pre-plotted . I want to delete the previous sampling stations (h1 handle) if they already exist and then plot the new sampling stations.

Below is my code:

if isexist(h1)
    delete(h1);
end

hold(app.mapPlot, 'on');

h1 = plot(app.mapPlot, lonlat(:,1), lonlat(:,2), 'o', 'color', 'b','markersize', 5);

Unfortunately, I got the below error:

Unrecognized function or variable 'h1'

Any idea on how to make this work?

Answer 1

[Joe Vinciguerra]

Try this... (note I'm using "exist" instead of "isexist")

clear % I'm starting with no 'h1'. This checks the "False" condition

if exist('h1')
    delete(h1); % if 'h1' is a thing, delete it
end

h1=plot([5 8],[12 11]); % now there is an 'h1' either way
hold on; % I insertered this to match your application
pause(3); % wait a few seconds to verify it visually

% Let's do it again to check the "True" condition
if exist('h1')
    delete(h1); % if 'h1' is a thing, delete it
end

h1 = plot([1 2],[2 4]); % still works

[Leon]

Many thanks! It works for your example. Weird enough, when I plug the code in my app-Designer script, it does not work (there is no error message anymore, but the lonlat stations are just not deleted).

if exist('h1')
    delete(h1);
end

if exist('h2')
    delete(h2);
end

hold(app.mapPlot, 'on');

h1 = plot(app.mapPlot, lonlat(:,1), lonlat(:,2), 'o', 'color', 'b','markersize', 5);

lonlat2 = [];
for i = min(b1,b2):max(b1,b2);
    if Sta{i}.lon>=20
        lon = Sta{i}.lon;
    else
        lon = Sta{i}.lon+360;
    end
    lonlat2 = [lonlat2; lon, Sta{i}.lat];
end

h2 = plot(app.mapPlot, lonlat2(:,1), lonlat2(:,2), 'ro', 'markerFaceColor', 'r', 'markersize', 5);

hold(app.mapPlot, 'off');

[Joe Vinciguerra]

I'm not as familiar with the app designer, but I'll try to help.

Are you sure it's really not deleting? Or is it deleting and replotting the same data quick enough that you don't notice?

Try another command instead of "delete". Perhaps "close"?

[Leon]

Many thanks! Weird enough, if I put the below code after the plot, it will delete the current sampling stations as expected. However, if I move it ahead of the plotting routine, the previously plotted sampling stations will remain there.

if exist("hh1")
    delete(hh1);
end