How to unfade legend placed on an empty (invisible) plot?

Question

Petar Milin 2024-3-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2100566-how-to-unfade-legend-placed-on-an-empty-invisible-plot

回答： Adam Danz 2024-3-29

I am trying to make a figure with three plots, and use the fourth one to place the legend. I set that last plot as invisible but then the legend is also faded. How can I fix that?

Here is the relevant code:

fig = figure();

subplot(1,4,1)

plot(x1(:,[1:15]),'LineWidth',3);

ylim([-0.3 1.2]);

title('X1');

subplot(1,4,2)

plot(x2(:,[1:15]),'LineWidth',3);

ylim([-0.3 1.2]);

title('X2');

subplot(1,4,3)

plot(x3(:,[1:15]),'LineWidth',3);

ylim([-0.3 1.2]);

title('X3');

subplot(1,4,4)

plot(x3(:,[1:15]),'Visible','off');

legend(labels,'FontSize',12,'Location','best');

axis off;

sgtitle('Lines');

set(fig,'Units','normalized','Position',[0 0 3 1.5]);

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Answer 1

Voss 2024-3-29

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Instead of making the lines in the last axes invisible, make them all-NaN so they don't show up but the legend stil appears normal.

% made up variables:

x1 = rand(10,15);

x2 = rand(10,15);

x3 = rand(10,15);

labels = "label"+(1:15);

% your code with last plot() modification:

fig = figure();

subplot(1,4,1)

plot(x1(:,1:15),'LineWidth',3);

ylim([-0.3 1.2]);

title('X1');

subplot(1,4,2)

plot(x2(:,1:15),'LineWidth',3);

ylim([-0.3 1.2]);

title('X2');

subplot(1,4,3)

plot(x3(:,1:15),'LineWidth',3);

ylim([-0.3 1.2]);

title('X3');

subplot(1,4,4)

plot(NaN(2,15));

legend(labels,'FontSize',12,'Location','best');

axis off;

sgtitle('Lines');

% set(fig,'Units','normalized','Position',[0 0 3 1.5]);

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Petar Milin 2024-3-29

在 MATLAB Online 中打开

Thanks! Can you please just unwrap (explain) why (2,15) in

plot(NaN(2,15),'LineWidth',3)

Voss 2024-3-29

在 MATLAB Online 中打开

OK. In that line you want to plot 15 lines (that's what you had originally), but I want them to be all NaNs. If I give plot a vector, then plot will give me one line only, so I need to use a matrix with 15 columns because plot plots one line per column of a matrix. The smallest matrix with 15 columns is 2x15, so that's what NaN(2,15) gives you, a 2x15 matrix of NaNs:

NaN(2,15)
ans = 2×15
   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN   NaN
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Answer 2

Adam Danz 2024-3-29

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It's much better to use tiledlayout than subplot.

With tiledlayout, the placement of the legend and the global title can be part of the layout.

fig = figure();
tcl = tiledlayout(1,4);  % <----- used tiledlayout
nexttile()              % <----- call nexttile instead of subplot
plot(x1(:,[1:15]),'LineWidth',3);
ylim([-0.3 1.2]);
title('X1');
nexttile()              % <----- call nexttile instead of subplot
plot(x2(:,[1:15]),'LineWidth',3);
ylim([-0.3 1.2]);
title('X2');
nexttile()              % <----- call nexttile instead of subplot
plot(x3(:,[1:15]),'LineWidth',3);
ylim([-0.3 1.2]);
title('X3');
leg = legend(labels,'FontSize',12,'Location','best');
leg.Layout.Tile = 4     % <----- assign legend to 4th tile location
title(tcl,'Lines');     % <----- Set the title of the entire layout instead of sgtitle
set(fig,'Units','normalized','Position',[0 0 3 1.5]);