Shuffling numbers from a list?

Question

Well, initially, I don’t know much about a C-list, but I have a list like int that will always have 4 elements that are: 1, 2, 3 e 4, I’m assigning them with the .Add, If anyone knows any other way, give me a hand..

I wanted to shuffle the items on this list always, that is, have a function to shuffle the items on the list and return me the shuffled list so I can use it.

Example:

A list: 1, 2, 3, 4

Return: 2, 1, 4 ,3 (randomly)

And after that, I have to use the elements of that list, how do I do that? In the example list the scrambled was 2, 1, 4, 3 how do I use each value of that in the code as an integer variable? Example: I want to assign a variable soma the value of the 1st and 3rd element of the shuffled list, as indicated by the 1st and 3rd element for the soma?

Answer 1

Here’s a simple solution:

var list = new List<int> {1, 2, 3, 4};
var rnd = new Random();

var query =
    from i in list
    let r = rnd.Next()
    orderby r
    select i;

var shuffled = query.ToList();

Answer 2

This answer teaches how to make some algorithms, such as Fisher-Yates, but it is important to note that this algorithm is not 100% random, according to the answer itself. The answer gives other more reliable solutions, but for simplicity purposes, I will keep only the first:

private static Random rnd = new Random();  

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

Use:

List<int> numeros = new List<int> { 1, 2, 3, 4 };
numeros.Shuffle();

To add the first to the third element, you can do as follows:

var soma = numeros[0] + numeros[2]; // 0 é a primeira posição, 2 é a terceira.

Answer 3

This reply already exists on the site since 21/05/2014. Actually this question is the duplicate. As it was opened and answered, I will answer too.

Note that I didn’t change the solution (here I took the part that improved the method to be able to choose which data range you want, but doesn’t change the execution itself), which is the important thing. I just took the example of the strings. If the problem is not knowing how to add elements of array, then the question should be this.

using static System.Console;
using System.Collections.Generic;

public static class Sorteio {
    public static void Main() {
        int[] array = { 1, 2, 3, 4 };
        array.Shuffle();
        foreach (var valor in array) WriteLine(valor);
        WriteLine("Soma: {0}", array[0] + array[2]); // soma 1o. e 3o. elemento
        //vamos de novo
        array.Shuffle(); //com poucos númros tem chance de repetir
        WriteLine($"Soma novo sorteio: {array[0] + array[2]}"); // soma 1o. e 3o. elemento
    }
}

namespace System.Collections.Generic {
    public static class IListExt {
        static Random r = new Random(DateTime.Now.Millisecond);

        public static void Shuffle<T>(this IList<T> list, int lowerItem, int upperItem) {
            upperItem = upperItem > list.Count ? list.Count : upperItem;
            lowerItem = lowerItem < 0 ? 0 : lowerItem;
            for (int i = lowerItem; i < upperItem; i++) {
                int j = r.Next(i, upperItem);
                T tmp = list[j];
                list[j] = list[i];
                list[i] = tmp;
            }
        }

        public static void Shuffle<T>(this IList<T> list, int upperItem) => list.Shuffle(0, upperItem);

        public static void Shuffle<T>(this IList<T> list) => list.Shuffle(0, list.Count);
    }
}

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.

To assign to a variable just do this:

var soma = array[0] + array[2]; //listas começam em zero então o elemento sempre é -1 ao desejado

For more details, see the answers already existing there in the original question.