randomly select different elements of a vector

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stephen cusack
stephen cusack 2016-7-21
评论： stephen cusack 2016-7-22
Hello,
I am looking to select n random elements from a vector, but none of the elements can be the same. for example x=[1 1 1 2 3 4 4 4 5 6 7 7], I want to select 4 random unique elements from x, giving 1, 4, 7, 6.
Thanks
Steve

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Thorsten
Thorsten 2016-7-22
x = [1 1 1 2 3 4 4 4 5 6 7 7];
for i = 1:4
ind = randperm(numel(x), 1); % select one element out of numel(x) elements, with the probability of occurrence of the element in x
r(i) = x(ind);
x(x==r(i)) = []; % delete this element from the sample, such that the picked elements are unique
end

更多回答（2 个）

the cyclist
the cyclist 2016-7-21
编辑：the cyclist 2016-7-21
x=[1 1 1 2 3 4 4 4 5 6 7 7];
ux = unique(x);
rx = randsample(ux,4,false);
Note that this will break if there are fewer than four unique elements in x, but it is easy to put in a safeguard against that. For example,
rx = randsample(ux,min(numel(ux),4),false);
  1 个评论
stephen cusack
stephen cusack 2016-7-22
Apologies I did not frame the question very well. I am looking to take the sample based on the occurrence of each element. So 1 has probability 3/12, 2=1/12, 3=1/12, 4=3/12, 5=1/12, 6=1/12, 7=2/12. Once one element has been chosen it cannot be selected again.

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Andrei Bobrov
Andrei Bobrov 2016-7-21
x=[1 1 1 2 3 4 4 4 5 6 7 7];
a = unique(x);
out = a(randperm(numel(a),4))
  1 个评论
stephen cusack
stephen cusack 2016-7-22
Apologies I did not frame the question very well. I am looking to take the sample based on the occurrence of each element. So 1 has probability 3/12, 2=1/12, 3=1/12, 4=3/12, 5=1/12, 6=1/12, 7=2/12. Once one element has been chosen it cannot be selected again.

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