如何在不耗尽内存的情况下在Matlab中使用randsample

Question

我想在Matlab中对1和n之间的m整数进行采样，而不替换，其中

m=10^6;
p=13^5;
n=p*(p-1)/2;

我已经尝试使用randsample如下

random_indices_pairs=randsample(n,m);

然而，我遇到了一个内存问题，那就是

Error using zeros
Requested 1x68929060278 (513.6GB) array exceeds maximum array size preference. Creation of arrays greater than this
limit may take a long time and cause MATLAB to become unresponsive. See array size limit or preference panel for more
information.
Error in randsample (line 149)
x = zeros(1,n); % flags

有办法避免这种情况吗？这里的问题是由于n是巨大的。

Answer 1

randperm的两个输入版本等效于randsample，没有替换，并且没有内存问题：

random_indices_pairs = randperm(n, m);

Answer 2

下面的脚本应该能满足您的需求。

• 它首先选取1到n范围内的m随机整数
• 然后检查是否有重复的条目
• 如果没有，脚本将停止
• 如果存在重复条目：
  • 它通过了所有这些
  • 在1和n之间找到另一个随机数
  • 检查整数数组中是否存在新的随机数
    • 如果是，它会找到另一个随机数
    • 如果没有，它将替换数组中的重复项，并移动到下一个重复项

%% Initialize
clearvars;
clc;
m = 10e6;
p = 13e5;
n = p*(p-1)/2;
%% Create m random integers between 1 and n
randomInt = randi(n, m, 1);
%% Find indices where duplicate random integers are
% Find indices of unique values, take the index of the first occurrence
[~, I] = unique(randomInt, 'first');
% Generate an array of all indices
dupIdx = 1:length(randomInt);
% Drop indices which point to the first occurrence of the duplicate
% This leaves indices that point to the duplicate
dupIdx(I) = [];
% Free up some memory
clear I;
if isempty(dupIdx)
disp('Done!')
else
% For those indices find another random number, not yet in randomInt
disp('Found duplicates, finding new random numbers for those')
counter = 0;
for ii = dupIdx
counter = counter + 1;
disp(strcat("Resolving duplicate ", num2str(counter), "/", num2str(length(dupIdx))))
dupe = true;
% While the replacement is already in the randomInt array, keep
% looking for a replacement
while dupe
replacement = randi(n, 1);
if ~ismember(replacement, randomInt)
% When replacement is unique in randomInt
% Put replacement in the randomInt array at the right index
randomInt(ii) = replacement;
dupe = false;
end
end
end
end

Answer 3

基于其中一条注释(该注释还建议了可能的改进(。

A=randi(n,m,1);
[U, I] = unique(A, 'stable');
A=A(I);
m_to_add=m-size(A,1);
while m_to_add>0
B=randi(n,m_to_add,1);
A=[A;B];
[U, I] = unique(A, 'stable');
A=A(I);
m_to_add=m-size(A,1);
end