boxplot

 

x1 = rand(20,6);
x2 = .5+rand(20,6);
x3 = randn(20,6);

x = [x1;x2;x3]; x = x(:);
g1 = [ones(size(x1)); 2*ones(size(x2)); 3*ones(size(x3))]; g1 = g1(:);
g2 = repmat(1:6,60,1); g2 = g2(:);

boxplot(x, {g2,g1},'notch','on', 'colorgroup',g1, 'factorgap',5, 'factorseparator',1)