Question about using randperm in a loop

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Veena Chatti
Veena Chatti 2020-3-9
评论： Veena Chatti 2020-3-10
Hi,
I'm using randperm in a loop that's meant to generate unique random three-digit numbers to fill a 5x5 matrix, r, like this:
for i = 1:length(r)
r(1:5,i) = (randperm(900,5) + 99);
end
My question is:
Is there a possibility of repeating a number given the function is being called 5 times, once for each column? I want each number to be unique.
Thanks,
Veena

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John D'Errico
John D'Errico 2020-3-10
编辑：John D'Errico 2020-3-10
So, you want to sample 5 sets of 5 numbers, all from the same set, but you want them to be unique? (The technical description would be to sample without replacement.)
The point is, you already know how to sample 5 such numbers. So just sample 25 numbers!
r = reshape(randperm(900,25) + 99,[5 5]);
There is no reason to need a loop.

更多回答（1 个）

James Tursa
James Tursa 2020-3-10
编辑：James Tursa 2020-3-10
If you want each number in the matrix to be unique, then don't call randperm( ) by row because that will not guarantee uniqueness between calls. Call randperm( ) only once for the entire matrix (25 elements) and then reshape to a 5x5. E.g., something like
r = reshape(randperm(900,25) + 99,5,5);

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