Add custom legend without any relation to the graph

34
votes

I wish to insert a legend that is not related to the graph whatsoever:

figure;
hold on;
plot(0,0,'or');
plot(0,0,'ob');
plot(0,0,'ok');
leg = legend('red','blue','black');

Now I wish to add it to another figure:

figure;
t=linspace(0,10,100);
plot(t,sin(t));
%% ADD THE LEGEND OF PLOT ABOVE
2
matlabmatlab-figurelegend
this is a simple example of a bigger thing I have so what you suggest is not relevant, there must be a way to do it - jarhead
So it is not clear what you want to achieve. Can you provide more information? Why do you need legend if there is no related data in the plot. - NKN
what I want to achieve is exactly what I wrote, use the box with the legend of the first figure, and have it displayed on the second - jarhead
2 hacky options: (1) add empty lineserie (or any empty graphic object) in the axes so that there are enough to populate the legend. (2, better in my view) make your own legend object (it's only a special axes object after all) which you can then move/copy/modify freely within your figures. Example on how to do that can be found here: plot-legend-title. - Hoki
You can even use NaN instead of 0 for your plot data. This way you don't even have to touch the visible property, nothing will be displayed anyway (the legend will still accept the data serie as a valid entry). - Hoki

2 Answers

44
votes

This is how I have solved this problem in the past:

figure
t=linspace(0,10,100);
plot(t,sin(t));
hold on;

h = zeros(3, 1);
h(1) = plot(NaN,NaN,'or');
h(2) = plot(NaN,NaN,'ob');
h(3) = plot(NaN,NaN,'ok');
legend(h, 'red','blue','black');

This will plot the additional points, but because the coordinates are at NaN they will not be visible on the plot itself:

enter image description here

EDIT 26/10/2016: My original answer results in greyed out legend entries in 2016b. The updated code above works, but the answer below is only relevant pre-2016b:

figure
t=linspace(0,10,100);
plot(t,sin(t));
hold on;

h = zeros(3, 1);
h(1) = plot(0,0,'or', 'visible', 'off');
h(2) = plot(0,0,'ob', 'visible', 'off');
h(3) = plot(0,0,'ok', 'visible', 'off');
legend(h, 'red','blue','black');

This will plot the additional points, but they will not be visible on the plot itself.

You can also use copyobj to copy graphics elements from one figure to another if you have a lot of elements, then use set(x, 'visible', 'off') to hide them before showing the legend, but it depends on what your final application is.

4
votes

Your question is a little unclear. However, the first thing I thought of when reading it was the text function in Matlab.

You can use the text function to add text to a Matlab figure. It's use is

>> text(x, y, str);

where x and y are the coordinates in the figure where you want to add the text str. You can use the Color option of text for colours and TeX to draw lines or even _. I've gotten very creative with plots using text.

Here's a quick and dirty example of emulating a legend with text

x = 0:pi/20:2*pi;
y = sin(x);
plot(x,y)
axis tight

legend('sin(x)');

text(5.7, 0.75, 'sin(x)');
text(5.1, 0.78, '_____', 'Color', 'blue');

which produces

             <code>text</code> example

For this specific case you could use the specific command (noted by @Hoki in the comments).

ht = text(5, 0.5, {'{\color{red} o } Red', '{\color{blue} o } Blue', '{\color{black} o } Black'}, 'EdgeColor', 'k');

to produce

             <code>text</code> example

by retrieving the handle to the text object it becomes trivial to copy it to a new figure, copyobj(ht, newfig). [1]