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MATLAB: legend for plotyy with multiple data sets
[m,n]=size(data1); %data1 - m x 3 matrix with data for first sample.
[ax,h1,h2]=plotyy([data1(1:m,1)],[data1(1:m,2)],[data1(1:m,1)],[data1(1:m,3)]);
  %plots 1st sample data

set(h1,'linestyle','o')
set(h2,'linestyle','o')
c1=get(h1,'color);c2=get(h2,'color'); %store colors

line('parent',ax(1),'xdata','[data2(1:m,1)],'ydata',[data2(1:m,2)],...
     'color',c1,'linestyle','s') %plots 2nd sample hardness
line('parent',ax(2),'xdata','[data2(1:m,1)],'ydata',[data2(1:m,3)],...
     'color',c2,'linestyle','s') %plots 2nd sample young's modulus

figure
hold all
for i=1:3
    h(i) = plot([i i])
end
ylim([0 4])

legend([h([1 3])], {'aa', 'cc'})