datacursormode: how to display info about current data point in relation to all data points on the same figure?

Hello! I am selecting multiple data points on the same figure using Data Cursor (Shift+Click). I would like that UpdateFcn displays if last selected data point (for example) has pair (i.e. if total number of data points is even). I have made some code but all I get is "unable to update data tip using custom update function". Thank you for any comments.

function getDataFromFigure1

fig = figure;
a = -16; t = 0:60;
plot(t,sin(a*t));

dcm_obj = datacursormode(fig);
set(dcm_obj,'UpdateFcn',@myUpdateFcn,'enable', 'on');

function txt = myUpdateFcn(~, event_obj)

          % read out all data points
            mypoints = getCursorInfo(dcm_obj);
            p=cell2mat({mypoints.Position}');
            N=size(pos(:,1),1);  

            if mod(N,2)==0
                txt = {'this data point does not have pair'};
            else
                txt = {'this data point has pair'};
            end

end
end

Answer 1

[Yair Altman]

You can get the clicked line object from event_obj.Target, and from there get the corresponding data points for the entire line:

function txt = myUpdateFcn(hDataTip, event_obj)
  % Get the clicked data coordinates
  clickedPoint = hDataTip.Position;  % [x,y,z] array
  % Now get all the data points on the clicked line
  hLine = event_obj.Target;  % or: hDataTip.DataSource or: hDataTip.Host
  xData = hLine.XData;  % 1xN array
  yData = hLine.YData;  % 1xN array
  zData = hLine.ZData;  % 1xN array
  ... % now do something useful with all this info
end

You can easily modify the code above to compare the clicked data point's coordinates to all the other data-points in the clicked line.

[David Rankin]

edited with solution that I found:

I have a similar problem but this code seems to solve it. I look at the Tag property to determine which line has been clicked on. Previously I was using IF statements and it was causing the error message.

However, the OTHERWISE case doesn't work as expected. If a plot is passed in without a tag named in the list, it returns an error message instead of the message in the OTHERWISE case. I would love to find out why this is happening but for now I will just make sure I cover the cases.

Here is my code:

   function txt = datatiptxt(~, hDatatip)

   pos = get(hDatatip, 'Position');
   t = get(hDatatip.Target, 'Tag');

   switch (t)
      case 'Temperature'
         val = pos(2);
         str = [num2str(val), ' C'];
         txt = {['Time: ', num2str(pos(1))], str};
      case 'Humidity'
         val = pos(2);
         str = [num2str(val), ' pct'];
         txt = {['Time: ', num2str(pos(1))], str};
      otherwise
         val = pos(2);
         txt = {["datatip: ', num2str(pos(1)), str);
  end
end

[Fritz]

Hi David

Error and warning messages do not seem to work inside the datatip update function.

And there is a syntax error in the second line of your OTHERWISE statement.

Should be:

   {['datatip: ', num2str(pos(1))], str};

Kind regards