Question

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Most efficient way to randomly “sort” (Shuffle) a list of integers in C#

How to effectively create a random copy of List<T>?

List<string> myList = new List<string>();
myList.Add("A");
myList.Add("B");
myList.Add("C");

// Now an extension method or a function which returns a random arrangement of myList:

List<string> GetRandomList()
{
    // List<string> result = new List<string>();
    // Random rnd = new Random();
    // Inside a loop
    // result.Add(myList[rnd.Next(1, myList.Count)]);
}

The extension method woud be public static List<T> Shuffle(List<T> this)

Answer 1

You are looking for a Shuffle, there are various implementations out there, usually the Fisher-Yates shuffle.

Below a generic implementation taken from here:

public static void Shuffle<T>(this IList<T> list)  
{  
    Random rng = new Random();  
    int n = list.Count;  
    while (n > 1) {  
        n--;  
        int k = rng.Next(n + 1);  
        T value = list[k];  
        list[k] = list[n];  
        list[n] = value;  
    }  
}

Note that this re-orders the list in place, it’s easy enough to refactor it to return a new list if that’s what you want to do.