Getting different colors for different numbers using `spy` in Matlab

Question

When I use spy to check a sparsity pattern, it doesn't distinguish certain elements from others. Is there any way to do this? Say, for example, elements that are equal to 10 are red and all elements equal to 9 are blue. Can I get this in one spy plot?

I've only been able to change the size and style of the plot points.

Answer 1

Here is how you can do it:

spy(a,'k')
hold on
spy(a==10,'r')
spy(a==9,'b')
hold off

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Another way is to use scatter instead of spy :

[x,y] = find(a);
clr = a(a~=0);
scatter(x,y,[],clr)
set(gca,'YDir','rev')

In this case the points will be colored by a values according to current figure colormap.