Adding the variable name onto a plot cursor

I regularly plot several variables. This results in 12 lines on a plot. For example with the x-axis being time, several channels of voltages are plotted. I can add a legend, but it's really hard to discern the different shades of blue or red or green to identify which curve is which. I want to add something in the data cursor callback function that will display the name of the selected line, so I can correlate the selected line with the legend box.

[Chandrashekar D S]

did you find any solution for this?

Answer 1

[Steven Lord]

I would consider using color, line style, and/or marker to distinguish the twelve lines. Using this example as inspiration:

% Make an axes
ax = axes;

% Change the ColorOrder and LineStyleOrder for the axes
% 3 values for ColorOrder
ax.ColorOrder = [1 0 0; % red
                 0 1 0; % green
                 0 0 1]; % blue
% times 4 values for LineStyleOrder gives 12 combinations
ax.LineStyleOrder = {'-o', '--*', ':', '-d'};

% Normally, calling plot resets axes properties
% Make it so it doesn't.
ax.NextPlot = 'replacechildren';

% Plot the 12 lines and show the legend. 
plot(magic(12))
legend show

Each line differs from the others in line style, color, and/or marker.

[S. Moore]

Since I regularly use data cursors - sometimes with custom data display, like 6 decimal points - using a callback function, it seems there should be a way to display the variable name in which the selected point belongs. The callback function uses the following to get the [X,Y] position of the data point:

 pos = get(event_obj,'Position');

All I need is something similar to:

 variablename = get(event_obj,'????');

where '????' is the one thing I need to know.

Answer 2

[Peter Meglis]

Take a look at the example halfway down this doc page: https://www.mathworks.com/help/matlab/ref/datacursormode.html

And this one for the get function: https://www.mathworks.com/help/matlab/ref/get.html

If you use datacursormode on your figure, you can get the cursor info, from that you can get the DisplayName (label) from the line you are focused on.

Something like:

fig = figure;
...
dcm_obj = datacursormode(fig);
...
c_info = getCursorInfo(dcm_obj);
disp(get(c_info.Target, 'DisplayName'));

Hope this helps!

[S. Moore]

Thank you Peter. I found this along with setting LineWidth on the graph to help identify the selected variable. However, this solution requires switching back and forth from the figure to the command console. Select datapoint with the cursor -> go to command window and view result -> back to figure window -> repeat. Using a callback function while in the figure window is the more interactive method.

I'm looking for a method to positively identify which line is being selected with the cursor within the figure window.

[Peter Meglis]

Take a look at this doc page for some examples: https://www.mathworks.com/help/matlab/creating_plots/callback-definition.html

If you supply the 'ButtonDownFcn' parameter with a function handle (@nameOfFunction) to your plot function, this callback will be called any time you click on one of the lines. The function must accept at least two arguments: "the handle of the object whose callback is executing" and "the event data structure" which can be empty like below.

...
plot(..., 'ButtonDownFcn', @displayNameOfLine);
...

function displayNameOfLine(src, ~)
  disp(get(src, 'DisplayName'))
end

From here you can do whatever you want in terms of displaying the DisplayName and including the datacursormode.

Hope this helps!

[Victor Braescu]

Thanks Peter! This helped with my problem where I had 500 different lines on my graph and wanted to see the legend name of each indivdually.

I edited it a bit to display the name directly on the graph and then delete the name after a second. I used text instead of disp to do this. Hopfully this helps anyone that is interested!

 function displayNameOfLine(src, ~)
  name = text(0.3,0.8,get(src, 'DisplayName'),'FontSize',50,'units','normalized');
  pause(1);
  delete (name);
 end