Editing variable through graph

Hi there, Is there a way to edit a variable through its plot? Take the following code:

x = rand(5,1); plot(x,'*')

this will produce a plot with five points. Is it possible to click on any of the points, drag them on the plot to a new location, and have Matlab update the variable x accordingly?

Thank you!

Answer 1

[Aashray]

Hi @MoHizzel!

I understand that you want to edit the contents of a variable x by dragging its plotted points so that the corresponding entries in x update automatically.

The issue with using a simple plot(x,'*') is that it only draws markers, which are not draggable by default.

The main change I made was to replace the static plot markers with “drawpoint” objects. Each data point is created as a draggable ROI, and I added listeners that trigger whenever a point is moved. Inside the callback, the x-coordinate is locked so that the index of the data point cannot change, only its y-value. The callback then updates the corresponding element of x and refreshes the line plot so that the results are immediately visible.

Here is my implementation for the same:

function drag_points 
% Initial data 
x = rand(5,1); 

% Figure and axes 
f = figure('Color','w'); 
ax = axes('Parent',f); hold(ax,'on'); box(ax,'on'); 
xlim(ax,[0.5 5.5]); 
xlabel(ax,'Index'); ylabel(ax,'Value'); 

% Line plot for context 
hLine = plot(ax, 1:numel(x), x, 'b-*', 'MarkerSize',8, 'LineWidth',1.2); 

% Make draggable points 
for k = 1:numel(x) 
    p = drawpoint(ax,'Position',[k x(k)],'Deletable',false); 
    addlistener(p,'MovingROI',@(src,evt) onMove(src,k)); 
    addlistener(p,'ROIMoved', @(src,evt) onMove(src,k)); 
end 

% Callback to update variable 
    function onMove(src,idx) 
        pos = src.Position; 
        pos(1) = idx;        % lock to index 
        src.Position = pos; 
        x(idx) = pos(2);     % update variable 
        hLine.YData = x;     % refresh line 
    end 
end  

<I have attached a video depicting the desired funcitonality.>

You can refer the documentation links below for more details:

• drawpoint: https://www.mathworks.com/help/images/ref/drawpoint.html
• addlistener : https://www.mathworks.com/help/matlab/ref/handle.addlistener.html