Question

I am currently using squeeze to remove two singleton dimensions from a matrix. The matrix is a large 4d matrix M(:,:,:,:). The first two dimensions are row and column coordinates (y and x). The variable in the third dimension (indexes) selects several values in the third dimension of M.

In a for-loop i am running, matrix M is adressed as M(y,x,indexes,:), which makes the first two dimensions singleton dimensions. These dimensions are then removed with squeeze for use in pdist, like so:

pdist(squeeze(M(y,x,indexes,:)))

Can i vectorize the use of squeeze in this case? (It takes up a lot of time in the loop)

Answer 1

If matrix M is not changed inside the loop, a simple solution is to reorder the matrix dimensions with PERMUTE before running for-loop:

Mperm = permute(M,[3 4 1 2]);

Then you can address Mperm instead of M as Mperm(:,:,y,x).