Adding the elements of the specified collection to the end of the List in C#

The AddRange() method in C# allows you to add all elements from a specified collection to the end of a List<T>. This method is more efficient than adding elements one by one using Add() when you need to append multiple items from an existing collection.

Syntax

Following is the syntax for the AddRange() method −

public void AddRange(IEnumerable<T> collection)

Parameters

• collection − The collection whose elements should be added to the end of the List. The collection itself cannot be null, but it can contain elements that are null.

Using AddRange() with String Arrays

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main(String[] args) {
      List<string> list = new List<string>();
      list.Add("Andy");
      list.Add("Gary");
      list.Add("Katie");
      list.Add("Amy");
      
      Console.WriteLine("Elements in List...");
      foreach (string res in list) {
         Console.WriteLine(res);
      }
      
      string[] strArr = { "John", "Jacob" };
      list.AddRange(strArr);
      
      Console.WriteLine("Elements in List...UPDATED");
      foreach(String str in list) {
         Console.WriteLine(str);
      }
   }
}

The output of the above code is −

Elements in List...
Andy
Gary
Katie
Amy
Elements in List...UPDATED
Andy
Gary
Katie
Amy
John
Jacob

Using AddRange() with Integer Arrays

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main(String[] args) {
      List<int> list = new List<int>();
      list.Add(25);
      list.Add(50);
      list.Add(75);
      list.Add(100);
      
      Console.WriteLine("Elements in List...");
      foreach (int val in list) {
         Console.WriteLine(val);
      }
      
      int[] intArr = { 150, 200, 250, 300 };
      list.AddRange(intArr);
      
      Console.WriteLine("Elements in List...UPDATED");
      foreach(int val in list) {
         Console.WriteLine(val);
      }
   }
}

The output of the above code is −

Elements in List...
25
50
75
100
Elements in List...UPDATED
25
50
75
100
150
200
250
300

Using AddRange() with Another List

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main(String[] args) {
      List<string> fruits = new List<string> { "Apple", "Banana" };
      List<string> moreFruits = new List<string> { "Orange", "Grapes", "Mango" };
      
      Console.WriteLine("Original fruits:");
      foreach (string fruit in fruits) {
         Console.WriteLine(fruit);
      }
      
      fruits.AddRange(moreFruits);
      
      Console.WriteLine("After AddRange:");
      foreach (string fruit in fruits) {
         Console.WriteLine(fruit);
      }
   }
}

The output of the above code is −

Original fruits:
Apple
Banana
After AddRange:
Apple
Banana
Orange
Grapes
Mango

Key Benefits of AddRange()

• Performance − More efficient than multiple Add() calls as it adds elements in bulk.

• Flexibility − Accepts any IEnumerable<T> collection including arrays, lists, and LINQ query results.

• Simplicity − Single method call instead of loops to add multiple elements.

Conclusion

The AddRange() method provides an efficient way to append multiple elements from any collection to a List in C#. It accepts arrays, other lists, or any IEnumerable collection, making it a versatile tool for combining collections efficiently.