How to add tooltips or overlay text in a Matlab fi

Question

I have a figure with two or more lines. These lines have additional, important information associated with them, like how many data points were averaged to create the line etc. I would like to access this information in my figure.

I thought a good solution for this would be to if you could hover over a line with your mouse and get that extended information.

However searching for tooltips/overlays/hover-over on figures seemed to not be fruitful.

Example:

figure; hold on;
plot(1:10,rand(10,1))
plot(1:10,rand(10,1))
% additional info
plot_1_info.name = 'Alice';
plot_2_info.name = 'Bob';
plot_1_info.age = 24;
plot_2_info.age = 12;

Any good solutions or better approaches for this?

Answer 1

Using the new data tip customization system introduced in R2019a, we can do the following:

figure(); hP = plot(1:10,rand(10,1),1:10,rand(10,1));
nPts = cellfun(@numel, {hP.XData});
hP(1).DataTipTemplate.DataTipRows(end+1) = dataTipTextRow('Name', repmat("Alice",nPts(1),1) );
hP(1).DataTipTemplate.DataTipRows(end+1) = dataTipTextRow('Age',  repmat(12,     nPts(1),1) );
hP(2).DataTipTemplate.DataTipRows(end+1) = dataTipTextRow('Name', repmat("Bob",  nPts(2),1) );
hP(2).DataTipTemplate.DataTipRows(end+1) = dataTipTextRow('Age',  repmat(24,     nPts(2),1) );
% (Of course the above can be organized in a nicer way using a function)

Which yields:

Notice that the "hover datatip" has black text, while the "click datatip" has blue text - this is default behavior.

Answer 2

You can change the data cursor behaviour, this option has good backwards compatability (I've tested the below in R2017b, used similar before in 15b).

See my comments for details:

% Create some data
x = (1:2:20).';
y = rand(10,1);
name = { 'Alice'; 'Alice'; 'Alice'; 'Alice'; 'Bob'; 'Bob'; 'Bob'; 'Chris'; 'Chris'; 'Chris' };
age = [ 24; 24; 24; 24; 12; 12; 12; 17; 17; 17 ];
% Put it in a table, so we have it all together for indexing as plot data
tbl = table( x, y, name, age );

% Create the plot, assign the UserData property to the plot object
f = figure; 
plt = plot( x, y );
plt.UserData = tbl;

% Hijack the Data Cursor update callback so we can inject our own info
dcm = datacursormode( f );
set( dcm, 'UpdateFcn', @onDataCursor );

% Function which returns the text to be displayed on the data cursor
function txt = onDataCursor( ~, evt )
    % Get containing figure
    f = ancestor( evt.Target, 'figure' );
    % Get the index within the original data
    idx = getfield( getCursorInfo( datacursormode( f ) ), 'DataIndex' );
    % The original data is stored in the UserData property
    data = evt.Target.UserData;
    % Each element of the cell array is a new line on the cursor
    txt = { sprintf( 'X: %g', data.x(idx) ), ...
            sprintf( 'Y: %g', data.y(idx) ), ...
            sprintf( 'Name: %s', data.name{idx} ), ...
            sprintf( 'Age: %g', data.age(idx) ) };          
end

Output:

Note: I've not handled anywhere the case that there is more than one data cursor tip. You can easily implement a loop over idx within the callback to handle this, I leave it as an exercise.

---

This approach is really flexible. For instance if we had 3 lines (one per 'person') then they can each have their own UserData struct, and we don't need to repeat all the info in table rows.

A = struct( 'X', 1:4, 'Y', rand(1,4), 'Name', 'Alice', 'Age', 24 );
B = struct( 'X', 1:3, 'Y', rand(1,3), 'Name', 'Bob', 'Age', 12 );
C = struct( 'X', 1:3, 'Y', rand(1,3), 'Name', 'Chris', 'Age', 17 );

f = figure; hold on;
plt = plot( A.X, A.Y ); plt.UserData = A;
plt = plot( B.X, B.Y ); plt.UserData = B;
plt = plot( C.X, C.Y ); plt.UserData = C;

% ... Now the struct fields can be accessed from the callback