Clean solution to shrink matrices

I have pre-allocated a large Matrix X = (80000,8). for e.g zeros(80000,8); This I did for speed. After several operations I only filled say 1000 rows of the matrix and remaining are all zeros as I pre-allocated all elements to be zero to start with. Now I would like the shrink the matrix to smaller one by eliminating all the trivial rows in the end. What is the cleanest way of doing them?

Answer 1

[Prema Gopalakrishnan]

X = X(1:n,:);

Answer 2

[John D'Errico]

As long as you know how many rows are filled (call it n, here n is 1000), then just do

X = X(1:n,:);