Generate random non-repeating integers from a small range

Question

What I\'m trying to accomplish is the following:

I wish to create a vector of integers, from a relatively small range, and ensure that none of the integers will be f

Answer 1

The kind of sequence you are looking for can be defined by generating differences from 1 to top - 1 and then computing the cumulative sum modulus top, starting from a random initial value:

function result = nonRepeatingRand(top, count)

    diff = randi(top - 1, 1, count);
    result = rem(cumsum(diff) + randi(1, 1, count) - 1, top) + 1;

end

On my machine, this generates a non-repeating sequence of 10 million numbers out of 1:5 in 0.58 seconds.

Answer 2

Do not regenerate the sequence every time, but fix the repetitions. E.g.:

function result = nonRepeatingRand(top, count)

    result = randi(top, 1, count);

    ind = (diff(result) == 0);
    while any(ind)
        result(ind) = [];
        result(end + 1 : count) = randi(top, 1, count - numel(result));

        ind = (diff(result) == 0);
    end

end

On my machine, this generates a non-repeating sequence of 10 million numbers out of 1:5 in 1.6 seconds.

Answer 3

How this?

top = 5;
count = 100;
n1 = nan;
out = [];
for t = 1: count 
    n2 = randi(top);
    while n1 == n2
        n2 = randi(top);
    end
    out = [out, n2];
    n1 = n2;
end

Answer 4

Taking the idea from A. Donda but fixing the implementation:

r=[randi(top,1,1),randi(top - 1, 1, count-1)];
d=rem(cumsum(r)-1,top)+1;

The first element of r is a randomly chosen element to start with. The following elements of r randomly choose the difference to the previous element, using modulo arithmetic.

Answer 5

you can use the following code for generate Non Repeating Random Numbers from 1 to M

randperm(M);

and for K Non Repeating Random Numbers from 1 to M

randperm(M, K);

enjoy