A simple clustering function that uses graph power for connectivity

clusterdemo.m

%% Example use of simplecluster

X = rand(20,2);
cutoff = .1;
[ Xf, class ] =simplecluster( X, cutoff );

h(1) = scatter( X(:,1), X(:,2), 50, class, 'filled');
set(h(1), 'MarkerEdgeColor','k')
hold on 
h(2) = plot( Xf(:,1), Xf(:,2), 'k+', ...
                               'Markersize', 14 );
grid on
hold off
title( sprintf('Points Connected within %f units', cutoff) , 'FontSize', 14 )
legend( h, 'Original', 'Clustered' )
axis equal
axis square
figure(gcf)

simplecluster.m

function [Xf, class] = simplecluster( X, cut )
% A simple clustering algorithm for point wise data
% X :: Column Matrix of Points
% cut :: Eucledean cutoff distance


%% Distance Matrix
D = pdist( X );
C1 = sparse( squareform( D <= cut ) + eye( size(X,1) ) );


%% Graph Power
% Compute Graph Power until the number of nonzero elements doesn't change

n1 = 0;

C = C1;
while n1 ~= nnz(C)
    n1 = nnz(C);
    C(:) = C1 * C';
end

%% Cluster original points
% Update clustered points

[ ~,un,class] =  unique( C, 'rows' );

Xf = zeros( numel( un ), size(X,2) );

for ii = 1 : size(X,2)
    Xf(:,ii) = accumarray( class, X(:,ii), [], @mean );
end