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

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Kelsey Shipman
Kelsey Shipman 2019-4-26
评论： Belinda Finlay 2020-5-28
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!

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回答（3 个）

Adam Danz
Adam Danz 2019-4-26
编辑：Adam Danz 2019-4-26
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)
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Adam Danz
Adam Danz 2019-4-27
编辑：Adam Danz 2019-5-15
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.

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Image Analyst
Image Analyst 2019-4-27
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;
0000 Screenshot.png
Kelsey Shipman
Kelsey Shipman 2019-4-29
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.

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