MATLAB: How to detect if a plot has already existed

isexistishghandleisnanMATLAB

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?

Best Answer

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
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