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Ashutosh Patel
Ashutosh Patel

Web Developer

I am a professional .NET developer with over 4 years of hands-on industry experience in designing, developing, and maintaining scalable web applications. I specialize in .NET Core, C#, RESTful APIs, and database-driven systems using SQL Server.

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1 Answers

Amrith Chandran
Amrith Chandran 13 Feb 2025
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LINQ Concat() in C#

The Concat() method in LINQ is used to combine two sequences (collections) into a single sequence without removing duplicates.

Basic Syntax

var CombineCollection = firstCollection.Concat(secondCollection);
  • Returns a new sequence that contains all the elements of firstCollection, followed by all the elements of secondCollection.
  • Does not modify the original collection.
  • Does not remove duplicates (unlike Union()).

Example with int type collection-

using System;
using System.Collections.Generic;
using System.Linq;
namespace MyConsoleApplication
{
   class MindStickSoft
   {
       static void Main()
       {
           List<int> numbers1 = new List<int> { 1, 2, 3 };
           List<int> numbers2 = new List<int> { 4, 5, 6 };
           var combined = numbers1.Concat(numbers2);
           Console.WriteLine("Concatenated List: " + string.Join(", ", combined));
           // Output: Concatenated List: 1, 2, 3, 4, 5, 6
       }
   }
}

The above program combines the two integer list into a new integer list.

Example with string type collection

using System;
using System.Collections.Generic;
using System.Linq;
namespace MyConsoleApplication
{
   class MindStickSoft
   {
       static void Main()
       {
           List<string> names1 = new List<string> { "Alice", "Bob" };
           List<string> names2 = new List<string> { "Charlie", "David" };
           var result = names1.Concat(names2);
           Console.WriteLine("Concatenated Names: " + string.Join(", ", result));
           // Output: Concatenated Names: Alice, Bob, Charlie, David
       }
   }
}

When to use Concat()

  • When you want to merge two collections while keeping duplicates.
  • When working with different types of sequences.
  • When you need to preserve the order of both collections.

Also, read: How to use DefaultIfEmpty() function in LINQ with C#? 

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