legend with multiple axes using yyaxis

I am creating a plot with two different y axes. the curves are added alternately. for example:

yyaxis left

plot(A)

yyaxis right

plot(B)

yyaxis left

plot(C)

yyaxis right

plot(D)

My problem is that when I add a legend to the plot, the order of the curves is not the order in which they were created. instead, they are ordered first by the left axis

and then by the right axis. meaning if i write down "legend(A,B,C,D)" the legend entry B will correspond with the curve C and vice-versa. is there a way to fix this? The actual case there are more than 4 curves, and the number changes every time, so manual changing is not possible. many thanks in advance

Nathan

Answer 1

[Star Strider]

Try this:

A = rand(1,10);
B = rand(1,15);
C = rand(1,20);
D = rand(1,30);

figure
hold on
yyaxis left
ha = plot(A);
yyaxis right
hb = plot(B);
yyaxis left
hc = plot(C);
yyaxis right
hd = plot(D);
hold off
legend([ha,hb,hc,hd], 'A','B','C','D')

Alternatively:

figure
yyaxis left
ha = plot(A);
hold on
hc = plot(C);
hold off
yyaxis right
hb = plot(B);
hold on
hd = plot(D);
hold off
legend([ha,hb,hc,hd], 'A','B','C','D')

Using hold is the only way to do what you want. This cannot be used with your posted code, because without the hold function, the second calls to yyaxis left and yyaxis right calls eliminate the handles to the previously plotted curves.

EDIT — (2 Jan 2021 at 17:41)

Added alternative code.

.

[Nathan Blanc]

Thank you Star. I didn't quite understand why you kept holding on and off in your code, but the naming of the plots and addition to the legend command solved my problem

Nathan

[Star Strider]

As always, my pleasure!

The hold function permits subsequent plots on the same axes, and that is necessary here. (I thought that I already posted a link to that function, however I now realise that did not, and have now corrected that. My apologies for the oversight.)

[Giovanni Bambini]

This does not seem to work when grouping bars:

A = [rand(10,1) zeros(10,1)];
B = [zeros(10,1) rand(10,1)];
figure;
yyaxis left
ha = bar(A, 'FaceColor', '#0000FF');
set(findobj(gcf,'type','axes'), 'ycolor', '#0000FF');
yyaxis right
hb = bar(B, 'FaceColor', '#00BCFF');
set(findobj(gcf,'type','axes'), 'ycolor', '#00BCFF');
legend([ha hb], 'h1', 'h2');

Warning: Ignoring extra legend entries.

Please help

E.

[Voss]

ha and hb are each 2 bar objects, as shown below. Therefore, [ha hb] is four bar objects. You can use just the first element of each ha and hb for the legend, [ha(1) hb(1)]

A = [rand(10,1) zeros(10,1)];
B = [zeros(10,1) rand(10,1)];
figure;
yyaxis left
ha = bar(A, 'FaceColor', '#0000FF')

ha = 
  1×2 Bar array:

    Bar    Bar

set(findobj(gcf,'type','axes'), 'ycolor', '#0000FF');
yyaxis right
hb = bar(B, 'FaceColor', '#00BCFF')

hb = 
  1×2 Bar array:

    Bar    Bar

set(findobj(gcf,'type','axes'), 'ycolor', '#00BCFF');
legend([ha(1) hb(1)], 'h1', 'h2');

[Giovanni Bambini]

Thanks!!!!

[Star Strider]

My pleasure!

A Vote would be appreciated!