生成具有范围的唯一随机Matlab数 [英] Generate Unique Random Matlab Numbers with a range

问题描述

说我想要1到10之间的5个数字.但是，我不想重复任何数字.我该怎么做?

Say I want 5 numbers between 1 to 10. However, I do not want any number to be repeated. How do I do this?

我想做

 randi([1,length(a)])

或者这个:

 (10-1).*rand(5,1) + 1

但是，这一次只能给我一个数字！我想要唯一的数字，这将无法保证.

But then, this only gives me one number at a time! I want unique numbers and this will nto guarantee it.

推荐答案

一种方法是使用randperm:

N = 10;    % Numbers from 1 to N will be permuted
n = 5;    % Numbers to be extracted
x = randperm(N);    % Permute numbers between 1 and N
x = x(1:n);    % Retain first n

这可以概括为任何一组值:

This can be generalized to any set of values:

N = 10;    % Length of vector of N numbers to be permuted
y = randn(N, 1);    % Vector from which you want to extract values
n = 5;    % Numbers to be extracted
x = randperm(N);    % Permute numbers between 1 and N
x = y(x(1:n));    % Retain first n of y

问题是当N大而n小时:

The problem is when N is large and n is small:

tic
N = 1e7;
n = 2;
x = randperm(N);
x = x(1:n);
toc

然后，您需要找到一个更好的解决方案.如果您有统计工具箱，请尝试:

Then you need to find a better solution. If you have the Statistics Toolbox, try:

tic
x = randsample(N, n, false);
toc

另一种方法，它也很慢，但是没有使用randperm或randsample:

Another approach, which is also slow but doesn't make use of randperm or randsample:

N = 1e7;
n = 2;
y = randn(N, 1);
tic
x = randn(N, 1);
[x x] = sort(x);
x = y(x(1:n));
toc

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