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C# / .NET - find duplicates in List using Linq

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Created by:

Veer-Ahmad

487

In this article, we would like to show you how to find duplicates in List with Linq in C#.

Quick solution:

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List<string> list = new List<string> { "A", "A", "B", "B", "B", "C", "D" };
​
List<string> duplicates = list.GroupBy(x => x)
                              .Where(y => y.Count() > 1)
                              .Select(z => z.Key)
                              .ToList();
​
// Result: ["A", "B"]

Practical example

Edit

In this example, we use Linq methods to find duplicates in the List.

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using System;
using System.Linq;
using System.Collections.Generic;
​
public class Program
{
    public static void Main()
    {
        List<string> list = new List<string> { "A", "A", "B", "B", "B", "C", "D" };
​
        List<string> duplicates = list.GroupBy(x => x)
                                      .Where(y => y.Count() > 1)
                                      .Select(z => z.Key)
                                      .ToList();
​
        foreach (string i in duplicates)
            Console.WriteLine(i);
    }
}