C# Concat Extension Method

You want to use the Concat extension method in your C# program. With the Concat method, you take two IEnumerable collections and then get a collection with all of the elements together. The Concat extension method effectively concatenates sequences.

Example

In this program, we include the System.Linq namespace to get access to the Concat method. Two arrays are created upon execution of the Main method; then, we call the Concat method twice, in different orders, and display the results each time.

This C# example program uses the Concat extension method from System.Linq.

Program that uses Concat extension [C#]

using System;
using System.Linq;

class Program
{
    static void Main()
    {
	int[] array1 = { 1, 3, 5 };
	int[] array2 = { 0, 2, 4 };

	// Concat array1 and array2.
	var result1 = array1.Concat(array2);
	foreach (int value in result1)
	{
	    Console.WriteLine(value);
	}
	Console.WriteLine();

	// Concat array2 and then array1.
	var result2 = array2.Concat(array1);
	foreach (int value in result2)
	{
	    Console.WriteLine(value);
	}
    }
}

Output

1
3
5
0
2
4

0
2
4
1
3
5

Usefulness. If you have ever needed to write custom code to combine two arrays or Lists into a single one, the Concat method might be useful for you. Instead of the custom code, you could use call Concat; please note that this might cause some performance degradation because of the flexibility and implementation of the extension methods.

Summary

Much like the string.Concat method concatenates strings, the Concat extension method concatenates sequences or collections. Whenever you need to combine two arrays into a third array, you can use the Concat extension method and avoid writing error-prone code.