Equal values in array

Question

How can I check if there are two or more equal values in one array?

eg. in this example, i want the program to tell me that there is a pair of 2 and a pair of 4

int[] array1 = { 1, 2, 4, 2, 4 };

Answer 1

Using Linq

var result = array1.GroupBy(i=>i)
                .Select(g=>new {Value = g.Key, Count = g.Count()})
                .Where(x=>x.Count>1)
                .ToList();

foreach (var pair in result)
{
     Console.WriteLine("PAIR: " + pair.Value + " COUNT: " + pair.Count);
}

Answer 2

[EDIT] Sorry, this answers the question "How can I check if there are two or more equal values in one array?", but it doesn't tell you the actual duplicates...

---

This would work, but possibly it isn't the most efficient way!

int[] array1 = { 1, 2, 4, 2, 4 };

if (array1.Distinct().Count() < array1.Length)
    Console.WriteLine("Contains Dupes");

If you want the most efficient approach:

bool containsDupes(int[] array)
{
    for (int i = 0; i < array.Length - 1; ++i)
    {
        int n = array[i];

        for (int j = i+1; j < array.Length; ++j)
            if (array[j] == n)
                return true;
    }

    return false;
}

I don't think you can get much more efficient than that. It will return as soon as it finds any match.

Answer 3

You could use a Linq Statement like:

            var query =
                from numbers in array1
                group numbers by numbers into duplicates
                where duplicates.Count() > 1
                select new { Item = duplicates.Key, ItemCount = duplicates.Count() };

This will return the following:

Item 2: ItemCount 2
Item 4: ItemCount 2

Or another syntax for the same:

var query = array1.GroupBy(x => x)
                  .Where(x => x.Count() > 1)
                  .Select(x => new { x, Count = x.Count() });

Answer 4

You could use LINQ's GroupBy

Example:

var grouped = array1.GroupBy(x => x).Select(x => new { Value = x.Key, Count = x.Count() });

foreach(var item in grouped) {
    if (item.Count == 1)
        continue;

    Console.WriteLine("There are {0} instances of the number {1} in the array.", item.Count, item.Value);
}

Answer 5

I like this syntax:

int[] array1 = { 1, 2, 4, 2, 4 };

var isThereAnyRepeated = (from i in array1
                            group i by i into g
                            where g.Count() > 1
                            select g).Any();

Console.WriteLine(isThereAnyRepeated);

Answer 6

Here's a slight variation of I4V's answer.

Instead of Select and ToList this uses ToDictionary.

using System;
using System.Linq;

namespace StackOverflow_2013_05_27_EqualValuesInArray
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] array = { 1, 2, 4, 2, 4 };

            var tbl = array
                .GroupBy(n => n)
                .Where(g => g.Count() > 1)
                .ToDictionary(g => g.Key, g => g.Count());

            foreach (var pair in tbl)
                Console.WriteLine("{0} is in array {1} times", pair.Key, pair.Value);

            Console.ReadLine();
        }
    }
}

Answer 7

class item
{
    int value;
    int number;
}
list<item> items = new list <item>();


for(int i=0; i<array1.length;i++)
{
    if (i=0)
    items.add(new item(array1[i],1))

    else if (array1.contains(array[i])) items.add(new item(array1[i],))
    else items.add(new item(array1[i],1))

}