The ability to plot a 3D GSCATTER plot is not available in Statistics Toolbox 7.2 (R2009b).
To workaround this issue, you can first call GSCATTER with just the X and Y data and capture the output argument (the handles to the object created). Following that, use the handles to set the 'ZData' property. Here is an example:
% create random dataset
x = randn(200,1);
y = randn(200,1);
z = randn(200,1);
g = [1*ones(50,1); 2*ones(50,1); 3*ones(50,1); 4*ones(50,1); ];
% call GSCATTER and capture output argument (handles to lines)
h = gscatter(x, y, g);
% for each unique group in 'g', set the ZData property appropriately
gu = unique(g);
for k = 1:numel(gu)
set(h(k), 'ZData', z( g == gu(k) ));
end
view(3)
