C# appointing distinct array elements randomly to another array

Question

First of all I am not an expert with C#, so I would appreciate answers that are simplied. And thanks in advance..

I have an array with 30 elements all integers and different than each other. I want to make an another array with length of 6. And appoint elements from 30length one to here but i dont want a number to appear more than one. I tried random function which obviously makes it possible to appear same numbers there. I could add statements maybe, but i thought there must be a short way.

I would like to ask you folks if there is, if so please share with me, thanks again.

int [] nums  = new int[30];
for (int i = 0; i < nums.Length; i++)
{
    nums[i] = i + 1;
}

Random rnd = new Random();
int[] card1 = new int[6];
for (int i = 0; i < card1.Length; i++)
{
    card1[i] = nums[rnd.Next(0, 30)];
}

Answer 1

So your problem, freely translated is:

I have a sequential, numeric array containing values from 1 through 30. I want to select 6 unique values from this array from random positions.

The accepted solution to this is to properly (e.g. Fisher-Yates) shuffle the array and simply take the number of required elements from the front.

Given you may want to keep your original array in order, you could create a copy and shuffle that.

That'll look like this:

var sourceArray = // your loop, or something like Enumerable.Range(1, 30).ToArray();
var arrayToPickFrom = Shuffle(sourceArray.ToArray()); // make a copy and shuffle it
var randomCards = arrayToPickFrom.Take(6); // take the first six elements 

Alternatively, the question could be simplified:

I want to generate N random, unique numbers between 1 and M.

Which is even less lines of code. But it all depends on your requirements. If you're actually trying to create a card game, where after the initial six cards more cards will be drawn - and a card can only be drawn once, you should approach this problem entirely different, for starters by introducing a Deck class to contain all cards, having convenient methods...

Answer 2

There are other ways to solve this, but since you asked for something simplified I will try not to change your code.

Random rnd = new Random();
var values = new List<int>(nums); // 1

int[] card1 = new int[6];
for (int i = 0; i < card1.Length; i++)
{
    var rand = rnd.Next(0, values.Count); // 2
    card1[i] = values[rand]; // 3
    values.RemoveAt(rand); // 4
}

1. Create a List from the nums array.
2. Take a random index;
3. Copy the element of the created list at that index to card1 array;
4. Remove the element from the list so you can't copy it again;

I must say that even though this is a simple solution, it is by no means the most "performant" one.

Answer 3

Why dont you take the first 6 ones?

var theOtherArray = Nums.Take(6).ToArray(); 

Answer 4

A simple solution:

int[] card1 = nums.OrderBy(it => Guid.NewGuid()).Take(6).ToArray();

Ordering the original array by a new guid should give you a decent approximation of randomness while avoiding the requirement to explicitly guard against duplication.

Then you just take the first 6 results.

Warning: The random-like behaviour of ordering by guid is an implementation detail of the current Guid.NewGuid() method so it's important not to rely on this functionality - especially in production code.

A better implementation would use a Fisher-Yates shuffle, see for example, this post: https://stackoverflow.com/a/1653204/5438433