It is interesting to look at the visualization of the MovieLens Rating Matrix
Here is a random sub sample
Here is the Matlab's code:
% load data
% Multi-character delimiters are not supported;
% so we get columns with delimeters too
D = importdata('ratings.dat',':');
% load data into sparse matrix
X = sparse(D(:,3),D(:,1),D(:,5));
% plot the whole matrix
imagesc(X'); figure(gcf)
% plot random sampling of matrix
r1_idx = randint(1,100,[1,6040]);
r2_idx = randint(1,100,[1,3592]);
R = X(r2_idx,r1_idx);
imagesc(R'); figure(gcf)