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Common legend for multiple histograms in subplots

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Laurent Chauvin
Laurent Chauvin on 9 Aug 2018
Commented: Laurent Chauvin on 10 Aug 2018
Hi,
I'm trying to display multiple histograms on several subplots (to avoid them overlapping too much), but I'd like to have only one legend for all of them.
I am aware of that post: https://www.mathworks.com/matlabcentral/answers/98474-is-there-a-command-in-matlab-for-creating-one-overall-legend-when-i-have-a-figure-with-subplots Unfortunately, that solution doesn't work when you plot histograms instead of plots. Here is the exact same code as proposed as a solution in the previously mentioned post, but with histograms instead of plots:
% Construct a figure with subplots and data
subplot(2,2,1);
line1 = histogram(rand(1,1000));
title('Axes 1');
subplot(2,2,2);
line2 = histogram(rand(1,1000));
title('Axes 2');
subplot(2,2,3);
line3 = histogram(rand(1,1000));
title('Axes 3');
subplot(2,2,4);
line4 = histogram(rand(1,1000));
title('Axes 4');
% Construct a Legend with the data from the sub-plots
hL = legend([line1,line2,line3,line4],{'Data Axes 1','Data Axes 2','Data Axes 3','Data Axes 4'});
% Programatically move the Legend
newPosition = [0.4 0.4 0.2 0.2];
newUnits = 'normalized';
set(hL,'Position', newPosition,'Units', newUnits);
The legend is set, but we cannot see the colors of the histograms in the legend except for the first one.
I looked for a while for a solution, but haven't found one yet.
Does anybody know how to do that?
Thank you

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Answers (1)

Thorsten
Thorsten on 9 Aug 2018
Set the FaceColor explicitly before calling legend:
set(line1, 'FaceColor', 'r')
set(line2, 'FaceColor', 'g')
set(line3, 'FaceColor', 'b')
set(line4, 'FaceColor', 'm')
hL = legend([line1,line2,line3,line4],{'Data Axes 1','Data Axes 2','Data Axes 3','Data Axes 4'});

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Laurent Chauvin
Laurent Chauvin on 9 Aug 2018
I'm sorry, what I meant by 'I cannot see the colors of the histograms' is that I cannot see them "in the legend". The histograms itself are properly colored. I guess your fix was to color histogram themselves, and not their rectangles in the legend.
However, I noticed this Warning / Error:
Warning: Error creating or updating Quadrilateral Error in value of property ColorData Array is wrong shape or size
So I think that's the reason why it cannot creates the small rectangles with the histogram colors in the legend, but I have no clue why I get this error.
Laurent Chauvin
Laurent Chauvin on 10 Aug 2018
Hum okay. I'm not sure to understand what is going on, but before I was calling 'legend' at the end of my script to create my histograms, and it wasn't working. However, now I removed it, and I use the 'legend' command when my script is done and has generated the histograms and it works.
Could this be a multithread issue (like legend is called before all my graphs are done, thus creating an issue) ?

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