How can I shuffle a list - list

Question

this code is for a game I create in unity. I have a list with 100 elements of coordinates and I want to instantiate boxes to them. The Amount of boxes should be 50% and totaly random. If I run my script, I get 50% of the boxes but in the default order. My script don't shuffle the elements in the list. Thanks for help!
// List has 100 elements of coordinates ( x & y)
public List<Vector2> ListPosBoxes = new List<Vector2>();
// Start
void Start()
{
AmountOfBoxes(ListPosBoxes);
}
// Method to display 50% shuffled boxes
void AmountOfBoxes(List<Vector2> list)
{
// Take list -> shuffle -> new list
list = ShuffleList(list);
for (int i = 0; i < list.Count/2; i++)
{
// Create Box
BoxGenerator(list[i]);
}
}
// Method to suffle list
List<Vector2> ShuffleList(List<Vector2> list)
{
Vector2 tmp;
// fisher–yates shuffle
for (int i = list.Count; i < 1; i--)
{
// Pick random Element
int j = Random.Range(0, list.Count);
// Swap Elements
tmp = list[j];
list[j] = list[i - 1];
list[i - 1] = tmp;
}
return list;
}
// Method to create Box
void BoxGenerator(Vector2 box)
{
CreateBox(box.x, box.y);
}
The problem is: the list isn't mixed.

Answer 1

You are running your for-loop from high numbers and decrease i.
// fisher–yates shuffle
for (int i = list.Count; i < 1; i--)
But the test in the for loop is i smaller than 1 so it never runs. Place a Debug.Log in the for-loop to test and flip the operator

Answer 2

I think the problem is that you are trying to re-declare a parameter.
For more info: https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/passing-parameters
Perhaps start with:
void AmountOfBoxes(List<Vector2> list)
{
// Take list -> shuffle -> new list
shuffled_list = ShuffleList(list);
for (int i = 0; i < list.Count/2; i++)
{
// Create Box
BoxGenerator(shuffled_list[i]);
}
}
// Method to suffle list
List<Vector2> ShuffleList(List<Vector2> list)
{
Vector2 tmp;
list *= list;
// fisher–yates shuffle
for (int i = list.Count; i < 1; i--)
{
// Pick random Element
int j = Random.Range(0, list.Count);
// Swap Elements
tmp = list[j];
list[j] = list[i - 1];
list[i - 1] = tmp;
}
return list;
}
I hope this helps.
What could also help you with debugging, is logging your variables someplace so that you know where it went wrong.

Answer 3

You have a couple of mistakes actually as mentioned in the previous answers but first of all, that Random.Range(0, list.Count); is quite biased actually, please check this link to have a better understanding of why.
And here is the corrected code:
// fisher–yates shuffle
for (int i = 0; i < list.Count; i++) {
// Pick random Element
int j = Random.Range(i, list.Count);
// Swap Elements
Vector2 tmp = list[i];
list[i] = list[j];
list[j] = tmp;
}