How can I drag points vertically in a plot?

Given a plot, I want to select a point in the plot and then drag it vertically in the plot using the mouse cursor.

Here is an example of my initial plot:

After drag the point it should look like this:

I already tried to use the brush function, but the best I can do is to get the coordinates of the selected points, but then I don’t know how to do the drag part.

Answer 1

[Akira Agata]

The solution would be like this. Please save the following code as an script file, and run it.

% Plot a line and points
figure
plot(1:10,1:10,'-o','buttondownfcn',{@Mouse_Callback,'down'});

% Callback function for each point
function Mouse_Callback(hObj,~,action)
persistent curobj xdata ydata ind
pos = get(gca,'CurrentPoint');
switch action
  case 'down'
      curobj = hObj;
      xdata = get(hObj,'xdata');
      ydata = get(hObj,'ydata');
      [~,ind] = min(sum((xdata-pos(1)).^2+(ydata-pos(3)).^2,1));
      set(gcf,...
          'WindowButtonMotionFcn',  {@Mouse_Callback,'move'},...
          'WindowButtonUpFcn',      {@Mouse_Callback,'up'});
  case 'move'
      % vertical move
      ydata(ind) = pos(3);
      set(curobj,'ydata',ydata)
  case 'up'
      set(gcf,...
          'WindowButtonMotionFcn',  '',...
          'WindowButtonUpFcn',      '');
end
end

[Kamil Dolinský]

Very nice. Thanks.

[Gregory Smith]

Hi Akira,

I'm working on some similar code and just found this. It looks brilliant but I'm struggling to understand how it works. I can't put breaks on it and go line by line to understand it for some reason.

Perhaps you could help me.

I'd like to modify the code you already wrote such when the user releases the mouse after moving a data point, the new Yvalues (after the user has altered them) are output to the MATLAB workspace.

Thank you!

[Panya Kansuwan]

Hi Akira,

Thanks for your answer. I have the same lase question as Gregory smith. Would you please inform how we can get updated y-data in workspace?

Best regards

[ska109]

I have modified Akira's answer in such way, that all parts of the code are functions. It's the similar way as GUIDE works. Data are exported to Workspace using ASSIGNIN function.

function Klikatko() % Based on https://www.mathworks.com/matlabcentral/answers/390704-how-can-i-drag-points-vertically-in-a-plot#answer_312006

if exist('hObject') == 0

% Inicializace

close all; clc;

handles = [];

handles.pl = [];

handles.plm = [];

% Plot a line and points

handles.figure_hlavni = figure;

handles.pl = plot(-3:3, (-3:3).^3, '-o');

handles.axis_hlavni = gca;

else

handles = guidata(hObject);

end

ExportData(handles.pl)

set(handles.pl, 'buttondownfcn', @Mouse_Callback_Down);

guidata(handles.figure_hlavni, handles);

end

function Mouse_Callback_Down(hObject,~,action)

handles = guidata(hObject);

xdata = get(handles.pl, 'xdata');

ydata = get(handles.pl, 'ydata');

pos = get(handles.axis_hlavni, 'CurrentPoint');

[~, handles.ind] = min(sum((xdata-pos(1, 1)).^2+(ydata-pos(1, 2)).^2, 1)); % Minimum součtu čtverců odchylek

delete(handles.plm);

hold on; handles.plm = plot(xdata(handles.ind), ydata(handles.ind), 'r-o');

set(handles.figure_hlavni,...

'WindowButtonMotionFcn', @Mouse_Callback_Move, ...

'WindowButtonUpFcn', @Mouse_Callback_Up);

guidata(handles.figure_hlavni, handles);

end

function Mouse_Callback_Move(hObject,~,action)

handles = guidata(hObject);

xdata = get(handles.pl, 'xdata');

ydata = get(handles.pl, 'ydata');

pos = get(handles.axis_hlavni, 'CurrentPoint');

ydata(handles.ind) = pos(1, 2);

set(handles.pl, 'ydata', ydata);

delete(handles.plm);

hold on; handles.plm = plot(xdata(handles.ind), ydata(handles.ind), 'r-o');

ExportData(handles.pl)

guidata(handles.figure_hlavni, handles);

end

function Mouse_Callback_Up(hObject,~,action)

handles = guidata(hObject);

set(handles.figure_hlavni,...

'WindowButtonMotionFcn', '',...

'WindowButtonUpFcn', '');

ExportData(handles.pl)

end

function ExportData(pl)

Data(1, :) = get(pl, 'xdata');

Data(2, :) = get(pl, 'ydata');

assignin('base', 'Data', Data); % https://www.mathworks.com/matlabcentral/answers/96201-how-do-i-access-a-base-workspace-variable-from-within-a-matlab-function

end