How to display legend for patch fill and plot lines at the same time in Matlab?

Question

I am trying to give legend to the whole plot. I know it sounds easy for many cases. But it makes me puzzled in this particular case.

figure;

p1 = plot(1:3,[y1,y2,y3],1:2,y4,1:3,[y5,y6,y7,y8,y9])

% Add lines
hold on
h1 = line([1 2 3],[10 10 10]);
h2 = line([1 2 3],[100 100 100]);
% Set properties of lines
set([h1 h2],'LineStyle','none')
% Add a patch
p2 = patch([1 3 3 1],[10 10 100 100],[.85 .85 .85],'LineStyle','none','FaceAlpha',0.5,'DisplayName','Lab Measurement');
hold off
set(gca, 'children',flipud(get(gca,'children')),'XTickLabel', {'L1' ' ' ' ' ' ' ' ' 'L2' ' ' ' ' ' ' ' ' 'L3'},'YScale', 'log')
NameArray = {'Marker','Color','LineStyle','DisplayName'};
ValueArray = {'o','[0.2 0.2 0.2]','-','Var1';...
    '+','[0.2 0.2 0.2]','-','Var2';...
    '*','[0.2 0.2 0.2]','-','Var3';...
    '.','[0.2 0.2 0.2]','-','Var4';...
    'x','[0.2 0.2 0.2]','-','Var5';...
    's','[0.2 0.2 0.2]','-','Var6';...
    'd','[0.2 0.2 0.2]','-','Var7';...
    '^','[0.2 0.2 0.2]',':','Var8';...
    'h','[0.2 0.2 0.2]','-.','Var9'};
set(p1,NameArray,ValueArray)

When I tried to reveal the legend by giving

legend(p1)

or

legend(p2)

This is what looks like when I try legend(p2)

It just did fine for each part, but not together.

I also tried by giving the legend in command

legend([p2 p1],{'Lab Measurement','Var1','Var2','Var3','Var4','Var5','Var6','Var7','Var8','Var9'})

or

legend([p2 p1],{'Lab Measurement',{'Var1','Var2','Var3','Var4','Var5','Var6','Var7','Var8','Var9'}})

It did not work. Any help would be greatly appreciated!

Answer 1

Per the documentation for plot :

h = plot(___) returns a column vector of chart line objects.

When multiple plot pairs are provided, as in your case, the return from plot is said array of objects:

>> a = plot(1, 2, 1, 2)

a = 

  2×1 Line array:

  Line
  Line

The bracket notation for concatenation [] generally implies the user wants to create a row vector, MATLAB does not make assumptions in the case of a vector and a scalar. This means it attempts to use horzcat to concatenate the arrays, which, logically, throws an error.

>> b = plot(1, 2); c = [a b];

Error using horzcat
Dimensions of matrices being concatenated are not consistent.

You'll need to explicitly tell MATLAB that you want to vertically concatenate these, or transpose the column vector into a row vector.

>> c = vertcat(a, b)

c = 

  3×1 Line array:

  Line
  Line
  Line

or:

>> c = [a.' b]

c = 

  1×3 Line array:

    Line    Line    Line

Both of which are compatible with legend .

Yay.

Answer 2

Just use

p = vertcat(p2,p1);
legend(p)

Problem solved. Thanks!