If I understand your question, the following may help
% create array like yours... n-by-5, last column has index of "bin" which
% will be in the set {1,2,...,maxIndex}
n = 10;
maxIndex = 5;
C = [rand(n,4),randi(maxIndex,n,1)];
% idx is a n-by-1 cell array where idx{j} contains the indices of rows
% belonging to bin j
idx = accumarray(C(:,5), 1:size(C,1),[],@(C){C});
% collect those rows from the matrix belonging to bin j into the jth cell
% of bins
bins = cellfun(@(x)C(x,:),idx,'uniformoutput',false);
