Get currently selected data point from axes in a figure - matlab

Question

I have a MATLAB figure with an axes containing a scatter plot.
Every point on this scatter plot has a signal data array associated with it.
I want to take user input as point selection from scatter plot and plot the corresponding signal data in another axes on the same figure.

Answer 1

Combine a global definition of your second axes with an UpdateFcn on the datacursor. See example below, which generates a sine wave based on a random variable selected.
function getSelectedDataPoint()
% create figure
fig = figure;
% make second axes a global to adress in myupdatefcn
global ax2
% define axes
ax1 = axes('parent',fig,'position',[0.05 0.05 0.9 0.4]);
ax2 = axes('parent',fig,'position',[0.05 0.55 0.9 0.4]);
% Random scatter
scatter(ax1,rand(25,1),rand(25,1),25,'filled')
% Set datacursormode to on
dcm_obj = datacursormode(fig);
datacursormode on
% Specify objective function for clock
set(dcm_obj,'UpdateFcn',#myupdatefcn)
% Define objective function
function text = myupdatefcn(~,obj)
text = sprintf('X: %f \n Y: %f',[obj.Position(1),obj.Position(2)]);
% Find corresponding signal
id = find(and(obj.Position(1) == obj.Target.XData,obj.Position(2) ==
obj.Target.YData));
% Do your thing with the signals
x = 0:0.1:100;
y = sin(obj.Target.XData(id)*x);
% plot on second axes
plot(ax2,x,y)
end
end

Answer 2

I am not sure I entirely understand what you want to do, but you might want to use the "Tag" option available for many objects in MATLAB.
Replace line under "Random scatter" by:
% Random scatter
hold(ax1,'on')
scatTag = cell(1,10);
for i = 1:10
scatTag{i} = scatter(ax1,rand(1,1),rand(1,1),25,'filled');
scatTag{i}.Tag = num2str(i);
end
In the data cursor update function, replace the line "id= find(..."
tagname = obj.Target.Tag;
And modify the signal function to point to your target tag, whatever function that is. In my example, you could do this to define the y-values:
y = sin(str2double(tagname)*x);
It will generate another sine wave, based on the tag.
Hope this helps :)