Unity freezing on play in "Rrandom number order" function

Questions & Answers
1

Hello,
I am making survey app in Unity. But have problem with function that are generating numbers from 0 to l-1 in random order, while storing them into list questionOrder.

Problem occurs (Unity freezing on play) when I put one specific condition in if statement bellow.

    int l = *someList*.Count; // Length I want my new integer list (questionOrder) to be
    int i = 0; // current length of *questionOrder* list
    while (i < l)
    {
        int r = Random.Range(0, l - 1);
        int k = 0;        

        while (i > 0 && k < questionOrder.Count && r != questionOrder[k])
        {
            k++;
        }

        if (i == 0 || k == questionOrder.Count) // *k < questionOrder.Count* is problematic
        {
            questionOrder.Add(r);
            i++;
        }
    }

First I am generating random number r, then with ‘nested while’ loop checking if generated number exists, if not ‘nested while’ will end because k == questionOrder.Count (r is compared with every list member, that means r is unique).
Then, in IF statement I am checking what was the reason ‘nested while’ ended (if k == questionOrder.Count then r is unique and will be added to questionOrder list).

If i remove k == questionOrder.Count and set i == 0 to i >= 0 (r does not need to be unique)
it works fine.

Note: i > 0 in ‘nested while’ and i==0 in if are just to work when the questionOrder list is empty.

2

If what you want is to randomize question order, you can use [Fisher–Yates shuffle Algorithm][1] to shuffle an array.

//this is where you have an array as lengt of l 
int l = *someList*.Count;
int[] arr = new int[l];
for(int i = 0; i < l; i++){
    arr *= i;*

}
arr = randomize(arr, l); //randomize

//Fisher–Yates shuffle Algorithm
static int[] randomize(int []arr, int n)
{
Random r = new Random();
for (int i = n - 1; i > 0; i–)
{
int j = r.Next(0, i+1);

int temp = arr*;*
arr = arr[j];
arr[j] = temp;
}
return arr;
}
_*[1]: https://www.geeksforgeeks.org/shuffle-a-given-array-using-fisher-yates-shuffle-algorithm/*_

3

With this statement:

int r = Random.Range(0, l - 1);

you can not generate “l” different random numbers since the number count you specify is “l-1”. So you will never hit your desired count. This is because Random.Range with integer parameters does exclude the upper limit. So Random.Range(0, 3) can return 3 different numbers 0, 1 or 2 but never 3.

Since your break condition is i >= l it will never be reached since the number range you draw from is one less than your desired target amount- So there’s no sequence of unique numbers which can do this.

Your line should have looked like this:

int r = Random.Range(0, l);