Randomly select samples from a matrix in proper order

Question

Shuo Zhang 2018-1-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/378963-randomly-select-samples-from-a-matrix-in-proper-order

评论： Shuo Zhang 2018-1-26

I have a 1 by 30000 matrix and I'd like to randomly select 300 elements from it. However, the selection should follow such a rule that if the previous selected element is the nth element in the matrix, then the next selection should be at least the n+1th element in the matrix. For example, if the first selection is the 5th element in the matrix, then the next selection should be done from the 6th element to the 30000th element, etc. I found out there's a command 'y = datasample(data,k)' that can take samples randomly, but what else should I do to ensure the right order?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

James Tursa 2018-1-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/378963-randomly-select-samples-from-a-matrix-in-proper-order#answer_301834

编辑：James Tursa 2018-1-26

在 MATLAB Online 中打开

Solution without repeats:

x = your vector
n = number of samples to select
y = x(sort(randperm(numel(x),n)));

If you have an earlier version of MATLAB, then that last part must be done in multiple steps:

r = randperm(numel(x));
y = x(sort(r(1:n)));

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Shuo Zhang 2018-1-26

This is quite amazing! Thank you very much!

请先登录，再进行评论。

Answer 2

Youssef Khmou 2018-1-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/378963-randomly-select-samples-from-a-matrix-in-proper-order#answer_301829

The selection procedure can be performed by ordering the inputs from the smallest to the largets, here is an example, a vector of N=4000 samples, we select randomnly P=100 points where the described rule is valid:

N=4000;

P=100;

x=rand(1,N);

Index=sort(round(N*rand(1,P)));

figure;

bar(Index);

y=x(Index);