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:
