[英]Implementing k-means algorithm correctly
我剛剛開始學習編碼,並開始編寫標准的k-means算法。 我在由三個不同的高斯生成的數據集上嘗試了實現,它似乎運行良好。 但是,我在虹膜數據集上進行了嘗試,然后不時(大約三分之一的時間)我的函數僅返回兩個集合,換句話說,它僅返回兩個簇。
我偷看了本地MATLAB kmeans函數的代碼,但由於缺乏編碼知識,最終迷失了自己。 我將非常感謝您的幫助!
function [R,C,P,it] = mykmeans(X,K)
% X -- data matrix
% K -- number of clusters
% C -- partition sets
% P -- matrix of prototypes
% R -- binary indicator matrix: R(i,j) specifies whether the ith data is
% classified into jth cluster
% it -- number of iterations until convergence
% N points with M dimensions
[N,M] = size(X) ;
%% Initialisation
% At this step we randomly partition the data matrix into K equally sized
% matrices and compute the centre of each of these matrices.
% I -- randomised index vector
% v -- number of data points assigned to each cluster
% U -- randomly partitioned matrices
v = N/K ;
C = cell(K,1) ;
U = cell(K,1) ;
I = randperm(N) ;
oldR = zeros(N,K) ;
% C{1} = X(I(1:v),:) ;
% U{1} = mean(X(I(1:v),:)) ;
for k=1:K
C{k} = X(I(1+v*(k-1):k*v),:) ;
U{k} = mean(C{k}) ;
end
P = cell2mat(U) ;
converged = 0 ;
it = 0 ;
while converged ~= 1
%% Assignment step
% Each element of D{n} contains squared euclidean distance of nth data
% point from the kth prototype
D = cell(N,1) ;
R = zeros(N,K) ;
for n=1:N
D{n} = sum((repmat(X(n,:),K,1) - P).^2,2) ;
[~,k] = min(D{n}) ;
R(n,k) = 1 ;
end
%% Update step
C = cell(K,1) ; % reset C
for k=1:K
for n=1:N
P(k,:) = R(n,k)*X(n,:) + P(k,:) ; % compute numerator of mean vector
if R(n,k) == 1
C{k} = [C{k};X(n,:)] ;
end
end
end
P = P ./ (sum(R)') ; % divide by denominator of mean vectors to get prototypes
%% Check for convergence
if sum(sum(R == oldR))==N*K || it == 100 % convergence criteria
converged = 1 ;
else
oldR = R ;
it = it+1 ;
end
end %while
實際上,該問題似乎不是編碼問題,而是理解k均值的問題。
實際上,在k均值期間,簇可能會變空。 您需要為此在代碼中說明,否則結果中的簇數可能小於k。
可能的解決方案可能是:
因此,一般方法如下:
在這里可以找到有關空集群問題的很好的說明。
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