Add a variable name to graphed points by selecting from a drop down menù

Hi to all,

I have a plot with some points and I need to assign a variable name to all these points. I would also like the variable name to be chosen from those available in a drop-down menu that opens when I click on the points themselves. Is it possible?

Answer 1

[VINAYAK LUHA]

Hi Gianmarco,

I understand that you want to annotate data points in a "scatter" plot in MATLAB, with text chosen from dropdown menu options, which appears on clicking the datapoints.

Here is a solution to achieve the above use case using nested callback functions –

1. Enable ‘data cursor’ mode using the “datacursormode” function, which allows interactive labelling of points by clicking on them.
2. Create a callback function named “showDropDown” and assign it to the “UpdateFcn” property of the “datacursormode” object.

• Inside the “showDropDown” function, use the “uicontrol” function to create a dropdown menu.
• Pass a function called assignVariableName as the callback to assign the selected text (annotation) to the data points.

For your better understanding, I am attaching the code snippet that demonstrates this approach:

% Create a figure and plot your points 
clc 
clear all 
close all 

f = figure; 
x = [1, 2, 3, 4, 5]; 
y = [2, 4, 1, 3, 5]; 
scatter(x, y); 
hold on; 

% Enable data cursor mode 
dcm = datacursormode(f); 
set(dcm, 'Enable', 'on'); 

% Create a callback function for the data cursor 
dcm.UpdateFcn = @showDropdown; 

% Callback function for the data cursor 
function output_txt = showDropdown(~, event_obj) 
    % Get the clicked data point 
    xClicked = event_obj.Position(1); 
    yClicked = event_obj.Position(2); 

   
    % Create a drop-down menu 
    variableNames = {'A', 'B', 'C', 'D'}; 
    dropdown = uicontrol('Style', 'popupmenu', 'String', variableNames, 'Position', [50, 40, 100, 20], 'Callback', @assignVariableName); 
    
    % Callback function for the drop-down menu 
    function assignVariableName(source, ~) 
        % Get the selected variable name from the drop-down menu 
        selectedVariable = variableNames{get(source, 'Value')}; 
        
        % Display the variable name on the graph 
        text(xClicked, yClicked, selectedVariable, 'Color', 'red',FontSize=50); 
        
        % Delete the drop-down menu 
        delete(dropdown); 
    end 
    output_txt = ""; 
end 

Further, you can refer to the following documentations of the functions used in the code snippet for more details:

1. datacursormode: https://www.mathworks.com/help/matlab/ref/matlab.graphics.shape.internal.datacursormanager.html
2. uicontrol: https://in.mathworks.com/help/matlab/ref/uicontrol.html

I hope you find the provided solution useful and this solution helps you label your data points according to your desired workflow.

Regards,

Vinayak Luha