MATLAB: Permanently set "Text Update Function" for Data Cursor in figures - matlab

Question

Problem: I use MATLAB for science, and I often need more than 4 significant digits. Every time I use Data Cursor in a figure's GUI, I need to manually right-click on the point, Select Text Update Function... or Edit Text Update Function..., and navigate to the folder where I saved the function whose callback prints more than 4 (e.g. 8) significant figures. This is annoying and there should be a way to automatically change this.
Ideal answer: I want this done permanently for all figures, e.g. in a function that changes default settings in my startup.m file.
Good enough answer: I want a wrapped function to which I give the figure handle and it fixes this for me.
I humbly await SO's infinite wisdom.

Answer 1

The permanent solution
would be, to edit the default_getDatatipText.m function.
You can find it in:
C:\...\MATLAB\R20xxx\toolbox\matlab\graphics\#graphics\#datacursor
There you will find the line:
DEFAULT_DIGITS = 4; % Display 4 digits of x,y position
Edit it as desired, you can't do much harm, but make a backup before if you want.
Alternative solution:
There is also the possibility of custom data tips: Tutorial at Matlab Central
It could finally look like this:
(additional text outside data-tips was post-processed)
And as you're talking about precision. The data-tip always snaps to the closest data-point. It doesn't show interpolated data at the clicked position.

Answer 2

The permanent answer given by thewaywewalk doesn't work anymore in R2015a, and probably later ones. So here I share my solution for both the temporary and permanent solution
Temporary solution (for a single figure):
The following function contains the update function as a nested function. Call datacursorextra to apply it to the current figure, or datacursorextra(fig) to apply it to some figure fig.
function datacursorextra(fig)
% Use current figure as default
if nargin<1
fig = gcf;
end
% Get the figure's datacursormode, and set the update function
h = datacursormode(fig);
set(h,'UpdateFcn',#myupdatefcn)
% The actual update function
function txt = myupdatefcn(~,event)
% Short-hand to write X, Y and if available Z, with 10 digit precision:
lbl = 'XYZ';
txt = arrayfun(#(s,g)sprintf('%s: %.10g',s,g), lbl(1:length(event.Position)), event.Position,'uniformoutput',false);
% If a DataIndex is available, show that also:
info = getCursorInfo(h);
if isfield(info,'DataIndex')
txt{end+1} = sprintf('Index: %d', info.DataIndex);
end
end
end
Permanent solution (apply to all figures by default):
I have not found a way to set a default UpdateFcn for the data cursor, but it is possible to add some code which will be called every time a new figure is created. Add the following line to your startup.m:
set(0,'defaultFigureCreateFcn',#(s,e)datacursorextra(s))
and make sure the datacursorextra function given above is available in your Matlab path.

Answer 3

#caspar's solution works very well.
You can also update the txt{} part of the solution with
if isfield(info,'DataIndex')
DataIndex = [info.DataIndex];
txt{end+1} = sprintf('Index: %d\n', DataIndex(1));
end
This will enable you to update the Index field when you have multiple pointers in the same figure.