How To Combine Two Lists Without Duplicate Values In C#

In this article, we will learn how to combine two lists without duplicate values in C#.

The Union() method is used to combine two lists with distinct values.

Combine int Lists

using System;
using System.Collections.Generic;
using System.Linq;

namespace Combine_Lists
{
    class Program
    {
        static void Main(string[] args)
        {
            var numberList1 = new List<int> { 10, 65, 4, 65, 33, 27, 10, 65 };
            var numberList2 = new List<int> { 1, 2, 3, 4, 3, 5, 5, 6 };
            var result = numberList1.Union(numberList2).ToList();
            result.ForEach(r => Console.WriteLine(r));
        }
    }
}

Output:

Combine string Lists

using System;
using System.Collections.Generic;
using System.Linq;

namespace Combine_Lists
{
    class Program
    {
        static void Main(string[] args)
        {
            var moviesList = new List<string> { "No Time to Die", "Wonder Woman 1984", "Bloodshot", "Black Widow", "Bloodshot" };
            var seriesList = new List<string> { "The Witcher", "Stranger Things", "Game of Thrones", "The Witcher" };
            var result = moviesList.Union(seriesList).ToList();
            result.ForEach(r => Console.WriteLine(r));
        }
    }
}

Output:

Combine Object Lists

Here the list contains objects of a custom class so we need to implement IEquatable, as shown below.

class Student : IEquatable<Student>
{
    public string Name { get; set; }
    public int Age { get; set; }

    public override int GetHashCode()
    {
        return (Name == null ? 0 : Name.GetHashCode()) ^ Age.GetHashCode();
    }
    public bool Equals(Student student)
    {
        return Name.Equals(student.Name) && Age.Equals(student.Age);
    }
}

IEquatable<T> Interface provides an equality check when there is only one way of comparing the objects.

Now, we can use the Union() method same as above.

using System;
using System.Collections.Generic;
using System.Linq;

namespace Combine_Lists
{
    class Program
    {
        static void Main(string[] args)
        {
            var studentList1 = new List<Student>();
            studentList1.Add(new Student { Name = "Steve", Age = 18 });
            studentList1.Add(new Student { Name = "Bill", Age = 25 });
            studentList1.Add(new Student { Name = "Steve", Age = 18 });
            studentList1.Add(new Student { Name = "Lary", Age = 30 });

            var studentList2 = new List<Student>();
            studentList1.Add(new Student { Name = "Steve", Age = 20 });
            studentList1.Add(new Student { Name = "Lary", Age = 42 });
            studentList1.Add(new Student { Name = "Bill", Age = 25 });

            var result = studentList1.Union(studentList2).ToList();
            result.ForEach(r => Console.WriteLine($"Name = {r.Name}, Age = {r.Age}"));
        }
    }
    class Student : IEquatable<Student>
    {
        public string Name { get; set; }
        public int Age { get; set; }

        public override int GetHashCode()
        {
            return (Name == null ? 0 : Name.GetHashCode()) ^ Age.GetHashCode();
        }
        public bool Equals(Student student)
        {
            return Name.Equals(student.Name) && Age.Equals(student.Age);
        }
    }
}

Output:

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