Why does my legend only display 50 entries?

I have a plot with more than 50 items and I would like to add a legend for all of them. The legend gets truncated at 50.

p = plot(magic(100));

labels = cellstr(num2str((1:100)'));

legend(p,labels)

 

Answer 1

[MathWorks Support Team]

Legends are currently limited to no more than 50 entries. Usually in plots with more than 50 features, the plot is so cluttered and the legend is so large that it is more advisable to select just a few key items to display in the legend.

If you do require more than 50 entries, the workaround is to create an additional legend. This requires creating an additional hidden axes.

First plot the original data.

p = plot(magic(100));

labels = cellstr(num2str((1:100)'));

legend(p(1:50),labels(1:50),'location','westoutside')

Next create an additional axes so that the figure can have two legends. Because the new legend needs information about the color of each line, it is necessary to copy the original lines to this new axes.

set(gcf,'NextPlot','add')

newAx = axes;

newP = copyobj(p,newAx);

legend(newP(51:100),labels(51:100),'location','eastoutside')

Now make the new axes and copied lines invisible. Normally, this would be done by setting the Visible property of each line to 'off', however this would gray out the corresponding entries in the legend. Instead, set the XData and YData properties of each line to NaN.

axis(newAx,'off')

set(newP,'XData',NaN,'YData',NaN)

[Eric Sargent]

Legend will cap the number of entries at 50 if no handles are specified. To have all objects in an axes show up, pass in their handles to the legend command.

p = plot(magic(100));
legend(p);

Answer 2

[Richard Mittleman]

This is an amazingly stupid way to have to do this

[Kishan Prudhvi Guddanti]

Agreed

[Stewart Smith]

agreed

[Walter Roberson]

In my experience if you do not change font size, text requires 19 pixels of height per row. 19*50 = 1950 pixels. Common monitor resolution is 1920 x 1280.

Higher resolution monitors are available, but are you relying on your users all having one?

[emehmetcik]

If the 'NumColumns' property is set to 1, legend with more than 50 entry is useless indeed. However using more than one column in the legend makes it possible to have a much larger number of lines to be presented 'in the legend'. Although it would be quite hard to produce a meaningful graph with that many lines present, I don't understand the hard coded limitation at 50.

[Brendan Murphy]

1) Agreed

2) 19*50 = 950 in most cases, rather than 1950. cat(2,'19','50') yields 1950 if that's what you're after. Also, big monitors are nice; most of us just want labels on our plots though.

3) The limit to 50 is artificial - why not just default to adding a 2nd column once the 50 trace cap is exceeded? Use cases exist for myriad plot traces on one figure, in which only one or a few traces may be interesting.

[Walter Roberson]

You are right, I made a multiplication mistake.

Answer 3

[Eric Sargent]

Legend will cap the number of entries at 50 if no handles are specified. To have all objects in an axes show up, pass in their handles to the legend command.

p = plot(magic(100));
legend(p); 

[Dev-iL]

The main problem with this workaround is that it doesn't work when specifying an axes handle as a first input. In other words, this fails:

hF = figure(); hAx = axes(hF);
p = plot(magic(100));
legend(hAx, p);

[Walter Roberson]

It gets the axes handles from ancestor(p, 'axes') so it does not need to be passed a handle axes.

[Dev-iL]

Thank you for pointing this out! This indicates a different problem, where the legend(target, ___) syntax has side effects that change the outcome of the funciton significantly. At the very least it's a documentation bug, but more likely a sign that the legend implementation is somewhat flawed.

Answer 4

[Dev-iL]

I suggest using the following undocumented feature for this:

hF = figure(); 
hAx = axes(hF);
plot(hAx, magic(100));
hL = legend(hAx, '-DynamicLegend');
set(hL, 'LimitMaxLegendEntries', false); % << Solution