Legend- if plot is empty?

Question

Meera 2015-6-26

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/225487-legend-if-plot-is-empty

回答： Kwin 2016-2-3

Hello,

I would like to how we can write legend for empty plots also. I have set of 4 to 5 plots. But some times among these plots, few plots values may be empty (x=NaN, y=NaN). if the plot is empty, then that the legend is not displaying. Rather this legend is displaying for next plots. How can I display legend for 5 plots even if 2nd or 3rd plot is empty.

Thanking you.

Meera

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Answer 1

Kwin 2016-2-3

3
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I ran into a similar problem when using contour plots, which can also be empty.

The solution I came up with is:

clear all
figure, hold all
fig{1} = contour(rand(10), [0.5 0.5], 'r');
fig{2} = contour(rand(0), [0.5 0.5], 'g');
fig{3} = contour(rand(10), [0.5 0.5], 'b');
name = {'fig1', 'fig2', 'fig3'};
used = {};
for k = 1 : numel(fig)
 if ~isempty(fig{k})
    used = {used{:}, name{k}};
 end
end
legend(used)

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Answer 2

Azzi Abdelmalek 2015-6-26

2
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https://ww2.mathworks.cn/matlabcentral/answers/225487-legend-if-plot-is-empty#answer_184147

在 MATLAB Online 中打开

x=nan and y=nan is not an empty plot.

x1=[1 2 3]
x2=[]
y1=[1 2 3]
y2=[]
x={x1,x2}
y={y1,y2}
for k=1:numel(x)
  if isempty(x{k})
      plot(nan,nan)
  else
      plot(x{k},y{k})
  end
  hold on
end
legend({'a' 'b'})
hold off

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Meera 2015-6-29

在 MATLAB Online 中打开

Hello,

I even did the same way. But in legend it is always taking top first legend even for 2nd data

if isempty(ref_zero) == true
    x_axes = NaN;
    y_axes = NaN;
    plot(x_axes,y_axes,'cs');
else
      x_axes = [];
      y_axes = [];
      for z = 1:length(ref_zero)
          x_axes = [x_axes xdata(ref_zero(z))];
          y_axes = [y_axes ydata(ref_zero(z))];
      end
  if volt_data(1)== 7
      plot(x_axes,y_axes,'bs');
    elseif volt_data(1)== 13.5
        plot(x_axes,y_axes,'gs');
    elseif volt_data(1)== 18
        plot(x_axes,y_axes,'ks');
    end
    hold on;
  end
plot(x,y_LL,'-r','LineWidth',2)
hold on;
plot(x,y_UL,'-r','LineWidth',2)
grid on;
l = legend('@empty','@ 7.0V','@ 13.5V','@ 18.0V','LL','UL','Location','NorthEastOutside'); 
hold off;