how to compare the elements of a single array between themselves

Question

I would like to compare the elements of a array fed by random values to see if this value has not been added a second time in my array

static void Main(string[] args)
{
    Random rand = new Random();

    int[] elements = new int[8];
    int lo = rand.Next(1, 49);
    for (int i = 0; i < elements.Length; i++)
    {
        lo = rand.Next(1, 49);
        elements[i] = lo;
    }

    for (int i = 0; i < elements.Length; i++)
    {
        if (elements[i] == elements[elements.Length - 2])
        {

        }
    }

    for (int x = 0; x < elements.Length; x++)
    {
        Console.WriteLine(elements[x]);
    }
}

Maybe you want to use standard `HashSet`? It guarantees that elements would be unique — nonForgivingJesus, Aug 01 '19 at 15:34
I think this is related, and even answered by @TimSchmelter https://stackoverflow.com/a/18304070/7002366 — FF-, Aug 01 '19 at 15:41

score 1 · Answer 1 · answered Aug 01 '19 at 15:37

1

var hasDuplicates = elements
    .GroupBy(entry => entry)
    .Select(group => new { Entry = group.Key, Count = group.Count() })
    .Where(group => group.Count > 1).Count() > 0;

answered Aug 01 '19 at 15:37

Ben Bancroft

95
10

score 1 · Accepted Answer · answered Aug 01 '19 at 16:11

The other answers correctly solves your problem of detecting if there are any duplicate entries using GroupBy. However, if your intent is to replace those duplicate entries with new non-existing entry in the array, you can use the methods below -

        Random rand = new Random();

        int[] elements = new int[8];
        int lo;
        for (int i = 0; i < elements.Length; i++)
        {
            do
                lo = rand.Next(1, 49);
            while (elements.Contains(lo));
            elements[i] = lo;
            Console.WriteLine(elements[i]);
        }

This code will guarantee that elements array will always have unique values.

Note :- do...while loop keep generating random numbers unless it finds a unique number. So if your array size is bigger then the range of random numbers generated you'll get stuck in an infinite loop.

thank you very much for your answer which is excellent and precise and which has met my expectations — AnTs, Aug 01 '19 at 16:51

score 0 · Answer 3 · answered Aug 01 '19 at 15:43

Using the power of linq you can use the GroupBy to find your duplicates.

Also, Enumerable.Range is a quick way of generating lists.

public static void Main()
{
    var rand = new Random();

    var elements = Enumerable.Range(0, 8).Select(_ => rand.Next(1, 49));

    var duplicates = elements.GroupBy(x => x).Where(x => x.Count() > 1).ToArray();

    if (duplicates.Any())
    {
        Console.WriteLine("duplicates found");  
    }
    else
    {
        Console.WriteLine("no duplicates"); 
    }
}

If you need to act on the duplicates you can iterate them and use .Key

how to compare the elements of a single array between themselves

3 Answers3