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)