How do I create a legend involving multiple plots created in a for loop?

I am trying to create a figure with 3 plots and a legend detailing what each plot is. Each plot is created in a for loop.

for j= 1:3

y = j;

figure(1);

plot(y);

hold on;

end

Thus, there will be 3 lines labeled in the legend. I appreciate any help that you all can provide!

Answer 1

[Adam Danz]

Here are some demos you can follow.

Option 1: add legend labels when you call legend

figure()
axes
hold on
nLoops = 3; 
ph = gobjects(1,nLoops); 
for j= 1:nLoops
    y = randn(10,1)+j; 
    ph(j) = plot(y, '-o');
end
legend(ph, {'first', 'second', 'third'})

Option 2: add legend labels within the loop

figure()
axes
hold on
nLoops = 3; 
ph = gobjects(1,nLoops); 
for j= 1:nLoops
    y = randn(10,1)+j; 
    ph(j) = plot(y, '-o', 'DisplayName', sprintf('line %d',j));
end
legend(ph)

[Kelsey Shipman]

Thank you so much for your answer!

Unfortunately, both options gave me the error "Unable to use a value of type 'matlab.graphics.chart.primitive.Line' as an index." on the line with legend

[Adam Danz]

What version of Matlab are you using? Did you get that error running my sample code or after adapting it to your code?

[Kelsey Shipman]

I got the error on your sample code and when I adapted it to my own.

MATLAB_R2019a

[Adam Danz]

I just triple-checked and the two demos I wrote function perfectly in 2019a. What was the error message?

Could you share a reproducible version of your code? I'm sure it's a small error; easy to fix.

Answer 2

[Image Analyst]

Try this:

figure()
hold on
numberOfLoops = 3; 
for k = 1 : numberOfLoops
    y = randn(10,1) + k; 
    plot(y, '.-', 'MarkerSize', 20, 'LineWidth', 2);
    % Make up a string for this particular line plot.
    legends{k} = sprintf('This is plot #%d', k);
end
legend(legends) % Display all the legend texts.
grid on;

[Belinda Finlay]

Thanks, you answer my question - before I even had to ask.

Answer 3

[Kelsey Shipman]

I appreciate all of your help. The problem was due to an undiagnosed error at the beginning of my script, so I have figured out the problem, and my legend is now displaying appropriately.