Changing the marker shape or aspect ratio in a legend

Consider the following example code, and the plot legend it creates:

% Example data 
means = [10 40 50 60; ...3 groups, each with 4 conditions (measures)
    20 50 60 70; ...
    30 60 80 90]; 
SEMs  = [1 4 8 6; ...
    2 5 9 12; ...
    3 6 10 13]; 
nGroups = size(means, 1);
nConditionsPerGroup = size(means, 2);
figure('Position', [71 433 560 420])
b = bar(means, 'grouped');
hold on
clear x
% Get the x coordinate of the bars
for i = 1:nConditionsPerGroup
    x(i,:) = b(i).XEndPoints;
    b(i).BarWidth = 1;
end
% Plot the errorbars
errorbar(x',means,SEMs,'k','linestyle','none');
hold off
set(gca, 'XTickLabel', {'Low' 'Middle' 'High'},  'FontSize', 12);
xlabel('Socio-economic status',  'FontSize', 18)
[leg,att] = legend('A', 'B', 'C', 'D',     'Orientation','horizontal',  'FontSize', 15);
title(leg,'Measures')
leg.Title.Visible = 'off';
box off
ax = gca;
ax.YGrid = 'on';

I'd like to change the aspect ratio of the legend markers to make them square instead of rectangular. Alternatively, to change their shape altogether and make them e.g. round.

However, I found no property inside the legend handle to manipulate aspect ratio or shape of the markers, only their size (`MarkerSize`). Changing the overall size (width/height) of the legend leaves aspect ratio unchanged.

Thanks for any help!

Answer 1

[DGM]

Here's one way. You might also want to adjust the text object positions as well.

% Example data 
means = [10 40 50 60; ...3 groups, each with 4 conditions (measures)
    20 50 60 70; ...
    30 60 80 90]; 
SEMs  = [1 4 8 6; ...
    2 5 9 12; ...
    3 6 10 13]; 
nGroups = size(means, 1);
nConditionsPerGroup = size(means, 2);

%figure('Position', [71 433 560 420])
b = bar(means, 'grouped');
hold on
clear x

% Get the x coordinate of the bars
for i = 1:nConditionsPerGroup
    x(i,:) = b(i).XEndPoints;
    b(i).BarWidth = 1;
end

% Plot the errorbars
errorbar(x',means,SEMs,'k','linestyle','none');
hold off
set(gca, 'XTickLabel', {'Low' 'Middle' 'High'},  'FontSize', 12);
xlabel('Socio-economic status',  'FontSize', 18)
[leg,att] = legend('A', 'B', 'C', 'D',     'Orientation','horizontal',  'FontSize', 15);
title(leg,'Measures')
leg.Title.Visible = 'off';
box off
ax = gca;
ax.YGrid = 'on';

% adjust each patch object in the legend
% patch vertex data is normalized WRT the legend box
textoffset = att(1).Position(1) - att(5).Children.Vertices(3,1);
leg.Units = 'pixels'; 
lp = leg.Position;
for k = 1:4
    V = att(k+4).Children.Vertices;
    xcent = mean(V(2:3,1))*lp(3);
    halfw = diff(V(1:2,2))/2*lp(4);
    V(:,1) = (xcent + halfw*[-1 -1 1 1 -1].')/lp(3);
    att(k+4).Children.Vertices = V;
    att(k).Position(1) = V(3,1) + textoffset;
end

Since the objects are just patches, I don't see why you couldn't make them into any polygonal shape you want.

Alternatively, you can also do other workarounds using dummy objects:

https://www.mathworks.com/matlabcentral/answers/1693100-putting-a-legend-on-a-fused-image

[z8080]

thank you! would making markers round be possible too, given that circles are not polygons?

[DGM]

As far as anyone will be able to tell, an appropriate polygon might as well be a circle.

% Example data 
means = [10 40 50 60; ...3 groups, each with 4 conditions (measures)
    20 50 60 70; ...
    30 60 80 90]; 
SEMs  = [1 4 8 6; ...
    2 5 9 12; ...
    3 6 10 13]; 
nGroups = size(means, 1);
nConditionsPerGroup = size(means, 2);

%figure('Position', [71 433 560 420])
b = bar(means, 'grouped');
hold on
clear x

% Get the x coordinate of the bars
for i = 1:nConditionsPerGroup
    x(i,:) = b(i).XEndPoints;
    b(i).BarWidth = 1;
end

% Plot the errorbars
errorbar(x',means,SEMs,'k','linestyle','none');
hold off
set(gca, 'XTickLabel', {'Low' 'Middle' 'High'},  'FontSize', 12);
xlabel('Socio-economic status',  'FontSize', 18)
[leg,att] = legend('A', 'B', 'C', 'D',     'Orientation','horizontal',  'FontSize', 15);
title(leg,'Measures')
leg.Title.Visible = 'off';
box off
ax = gca;
ax.YGrid = 'on';

% adjust each patch object in the legend
% patch vertex data is normalized WRT the legend box
nsides = 100; % pick any regular polygon
theta = (0:360/nsides:360) + 360/nsides/2;
textoffset = att(1).Position(1) - att(5).Children.Vertices(3,1);
leg.Units = 'pixels'; 
lp = leg.Position;
for k = 1:4
    % replace patch object with a regular polygon
    V = att(k+4).Children.Vertices;
    patchcent = [mean(V(2:3,1)) mean(V(1:2,2))].*lp(3:4);
    radius = diff(V(1:2,2))/2*lp(4);
    V = patchcent + radius*[cosd(theta.') sind(theta.')];
    V = V./lp(3:4);
    att(k+4).Children.Vertices = V;
    att(k+4).Children.Faces = 1:numel(theta);
    
    % move text label
    att(k).Position(1) = V(3,1) + textoffset;
end

[z8080]

beautiful work!!