MATLAB Plot - Legend entry for multiple data rows - getcolumn

Question

Consider the following example:

x = magic(3);
figure(1); clf(1);
plot( x, '-r', 'DisplayName', 'Magic' );
legend( 'show' );

The resulting legend entries in MATLAB R2014a are
getcolumn(Magic,1)
getcolumn(Magic,2)
getcolumn(Magic,3)

The problem stems from function [leg,labelhandles,outH,outM] = legend(varargin) in legend.m (Copyright 1984-2012 The MathWorks, Inc.), line 628:
str{k} = get(ch(k),'DisplayName');
More specifically, the function get

prepends getcolumn( and
appends , <Column Number>).

Is there an easy way to display exactly one legend entry (or multiple, but without the pre- and appended strings) for multiple data rows named after DisplayName, which have the same visual properties?

An alternative would of course be to programatically create multiple (or one) legend entries through plot handles (see below), but I would like to keep things short and simple.

One entry:

x = magic(3);
figure(1); clf(1);
h = plot( x, '-r' );
legend( h(1), 'Magic' );

Multiple entries:

x = magic(3);
figure(1); clf(1);
h = plot( x, '-r' );
strL = cell( 1, numel(h) );
for k = 1:numel(h)
    strL{k} = sprintf( 'Magic %d', k );
end
legend( h, strL );

In MATLAB R2014b, the problem with getcolumn(Name,Row) does not appear anymore for the first code example.

EBH EBH · Accepted Answer · 2017-08-05T20:09:29

If you want to set multiple display names for the legend entries in short syntax, you just need to prepare a cell array with them, let's say it's called leg_names, and then use set to apply them to all at once:

set(p,{'DisplayName'},leg_names);

Let's take a look at an example:

x = magic(3); % your data
p = plot( x,'-r'); % plot and get an array of handles to the lines
% create a list of the desired names for the legend entries:
leg_names = [repmat('Magic ',size(x,2),1) num2str((1:size(x,2)).')];
set(p,{'DisplayName'},cellstr(leg_names)); % set all display names
legend('show'); % show the legend

The result is exactly as in your examples at the end of the question.

Also, note that the syntax: [lgd,icons,plots,txt] = legend(___) is not recommended (from the docs):

Note: This syntax is not recommended. It creates a legend that does not support all graphics features. Instead, use the lgd = legend(__) syntax to return the Legend object and set Legend Properties.

MATLAB Plot - Legend entry for multiple data rows - getcolumn

1 Answers