Given a vector, I would like to sample without replacement elements from it repeatedly.
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Given a (m x 1) vector v , I would like to ,randomly without replacement, sample s elements from it. I know I can use randsample(v,s) if I were to do this once. However, I want to do this repeatedly without using a for loop (i.e vectorization) so that it is fast.
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采纳的回答
Matt J
2020-8-21
m=10; n=15; s=3;
V=rand(m,n); %hypothetical data
[~,ids] = sort( rand(size(V)) ,1);
ids=ids(1:s,:)+m*(0:n-1);
selection=V(ids) %selects s elements from each column of V
4 个评论
Cem Gormezano
2020-8-21
Slower than the loop? Not on my machine,
m=10; n=1e6; s=3;
V=rand(m,n);
tic;
[~,ids] = sort( rand(size(V)) ,1);
ids=ids(1:s,:)+m*(0:n-1);
selection=V(ids);
toc; %Elapsed time is 0.306036 seconds.
tic
for i=1:n
randsample(V(:,i),s);
end
toc%Elapsed time is 4.263803 seconds.
Cem Gormezano
2020-8-21
Matt J
2020-8-21
You're quite welcome, but please Accept-click the answer if it resolved your issue.
更多回答（1 个）
Bruno Luong
2020-8-21
编辑：Bruno Luong
2020-8-21
v = 'a':'z' % your vector
n = 10; % number of "loop"
s = 3; % number of drawing without replacement
[~,ir] = maxk(rand(n,length(v)),s,2);
r = v(ir)
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