how to create a matrix of concatenated images

Hello i have 40 subfolders in a folder .each folder contains 10 images of a particular individual.I have created a image set of these folders labeled s1-s40.Now i have applied my normalisation fucntion to all these images by the help of imageset.I now want to convert the 2d normalised images into an 1d vector

     imdataloc='D:\x\orl_faces';

   facedatabase=imageSet(imdataloc,'recursive');

     output=normalised image

    so     
         output=output(:);

and i want to store this vector in the form a matrix for all the images (400 images) as columns . ie the rows indicate the size of the matrix of each image and columns indicate the images it is going to be an Nx400 matrix.

how do I do that in my imageset?