MATLAB: Question about using randperm in a loop

Question

Hi,

I'm using randperm in a loop that's meant to generate unique random three-digit numbers to fill a 5×5 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

Answer 1

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.