How to set a legend with a label for two or more lines?

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Lemuel Carlos Ramos Arzola
回答： Laurens 2024-10-31，15:10
Hello,
In the graphic legend I want to share the same label for two or more lines.
For example, I have two (or more) pair of data
x = linspace(0,0.5);
for i = 1:3
y1(i,:) = x.^2 + i;
y2(i,:) = (2*x).^2 + i;
end
My plot instructions are
hold on
plot(x,y1,'-')
set(gca,'ColorOrderIndex',1)
plot(x,y2,'--')
legend({'label 1','label 2','label 3'})
I want that the first curves of y1 and y2 share the label “label 1” and so on for the second and the thirds lines, “label 2” and “label 3”, respectively. Something like this
figure2.png
Thanks in advance for the answers.
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Lemuel Carlos Ramos Arzola
Lemuel Carlos Ramos Arzola 2020-2-7
Excellent alternative solution.
Thanks
(but the actual problem is unsolved)
Adam Danz
Adam Danz 2020-2-7
I understand. Walter pointed you to a function on the file exchange that might be helpful in building a custom legend.

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采纳的回答

Jeremy
Jeremy 2020-2-7
This isn't a particularly elegant solution, but I think it does what you want.
x = linspace(0,0.5);
for i = 1:3
y1(i,:) = x.^2 + i;
y2(i,:) = (2*x).^2 + i;
end
hold on
plot(x,y1,'-')
set(gca,'ColorOrderIndex',1)
plot(x,y2,'--')
[lh, labelhandles] = legend({'label 1','label 2','label 3'});
labelhandles(5).LineStyle = '--';
labelhandles(4).YData = [0.83 0.83];
labelhandles(5).XData = [0.0460 0.5057]; labelhandles(5).YData = [0.760 0.760];
This will only update one of the legend entries, I trust you can extend this solution to the others. You could also choose a labelhandles variable with a shorter name to make it look a little neater, if you wanted.
Your YData property can be tweaked until you are happy with the appearance.
plot_legend.png
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Lemuel Carlos Ramos Arzola
Lemuel Carlos Ramos Arzola 2020-2-7
编辑：Lemuel Carlos Ramos Arzola 2020-2-7
Very good idea Jeremy!
A little bit complex but it tackled the problem. I will be working with the legend function outputs to generalize your idea in my actual code.
I hope in the future Matlab automates this issue.
Thanks a lot.
Dear Adam thanks for the "note of caution", very important too.
I love Matlab and now I also love the community.
Best,
Lemuel

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更多回答（1 个）

Laurens
Laurens 2024-10-31，15:10
I understood the problem as follows: One legend entry can correspond to many lines on the graph. But Matlab assigns the first legend entry to colors/markers of the first line on the graph, the second entrie's colors/markers correspond to the second line in the graph and so on.
My solution therefore was to tell Matlab exactly - for each group of lines - which line belongs to which entry. you only have to do this once for each legend entry.
Exemple code:
figure
p1 = plot(x, y3, 'LineWidth', 0.3, 'Color', [0.4, 0.4, 0.4, 0.05]);
hold on
p2 = plot(x, y1, 'LineWidth', 2, 'Color', [1, 0, 0, 0.1]);
hold on
p3 = plot(x, y2, 'LineWidth', 5, 'Color', [0.9, 0, 0, 1]);
legend([p1(1,:); p2(1,:); p3(1,:)], {'entry 1','entry 2', 'entry 3' }, "Location","southoutside")
p1(1,:) samples one line (the first) from the first group of lines
p2(1,:) samples one line from the second group of lines
and so on ...

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