The standard way to compute the number of unique entries in a matlab matrix A is:
numel(unique(A))
If our entries are positive integers, we can try to do the same thing using sparse with:
nnz(sparse(A(:),1,1,size(A,1),1))
but actually this is slower.
I don't see a way to avoid a sort. I came up with this,
sum(diff(sort(F(:)))~=0)+1
As far as I can tell, this will work for matrices that don't have infs and nans. It's slightly faster than number(unique(A)). I have a feeling I'm only winning anything here because I'm avoiding overhead within unique