How to generate specific number of specific integers within a range?

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Doobie 2017-4-27

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https://ww2.mathworks.cn/matlabcentral/answers/337724-how-to-generate-specific-number-of-specific-integers-within-a-range

评论： Doobie 2017-4-28

I want to generate a random array of 8 integers within [1,4] where each integer appears exactly twice. Examples:

1 2 2 3 3 4 4
2 1 2 3 1 3 4
4 1 2 3 4 3 1

I know randi(4,8,1) gives a random array of 8 integers within [1,4] but it does not specify how many come from which integer. Is there a built in matlab function that does this? If not, what should I do?

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Answer 1

Stephen23 2017-4-28

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编辑：Stephen23 2017-4-28

在 MATLAB Online 中打开

This is easy with randperm:

>> vec = repmat(1:4,1,2);
>> out = vec(randperm(numel(vec)))
out =
   2   3   2   4   1   1   4   3
>> out = vec(randperm(numel(vec)))
out =
   1   4   2   3   2   1   3   4
>> out = vec(randperm(numel(vec)))
out =
   2   1   2   4   3   3   4   1