C# | How to remove the element from the specified index of the List

List<T>.RemoveAt (Int32) Method is used to remove the element at the specified index of the List<T>.

Properties of List:

• It is different from the arrays. A list can be resized dynamically but arrays cannot.
• List class can accept null as a valid value for reference types and it also allows duplicate elements.
• If the Count becomes equals to Capacity then the capacity of the List increases automatically by reallocating the internal array. The existing elements will be copied to the new array before the addition of the new element.

Syntax:

public void RemoveAt (int index);

Parameters:

index: It is the zero-based starting index of the element which is to be removed.
count: It is the number of the elements which is to be removed.

Exceptions: This method will give ArgumentOutOfRangeException if the index is less than 0 or equal to or greater than Count.

Below programs illustrate the use of List<T>.RemoveAt (Int32) Method:

Example 1:

// C# Program to remove the element at
// the specified index of the List<T>
using System;
using System.Collections;
using System.Collections.Generic;

class Geeks {

    // Main Method
    public static void Main(String[] args)
    {

        // Creating an List<T> of Integers
        List<int> firstlist = new List<int>();

        // Adding elements to List
        firstlist.Add(17);
        firstlist.Add(19);
        firstlist.Add(21);
        firstlist.Add(9);
        firstlist.Add(75);
        firstlist.Add(19);
        firstlist.Add(73);

        Console.WriteLine("Elements Present in List:\n");

        int p = 0;

        // Displaying the elements of List
        foreach(int k in firstlist)
        {
            Console.Write("At Position {0}: ", p);
            Console.WriteLine(k);
            p++;
        }

        Console.WriteLine(" ");

        // removing the element at index 3
        Console.WriteLine("Removing the element at index 3\n");

        // 9 will remove from the List
        // and 75 will come at index 3
        firstlist.RemoveAt(3);

        int p1 = 0;

        // Displaying the elements of List
        foreach(int n in firstlist)
        {
            Console.Write("At Position {0}: ", p1);
            Console.WriteLine(n);
            p1++;
        }
    }
}

Output:

Elements Present in List:

At Position 0: 17
At Position 1: 19
At Position 2: 21
At Position 3: 9
At Position 4: 75
At Position 5: 19
At Position 6: 73
 
Removing the element at index 3

At Position 0: 17
At Position 1: 19
At Position 2: 21
At Position 3: 75
At Position 4: 19
At Position 5: 73

Example 2:

// C# Program to remove the element at
// the specified index of the List<T>
using System;
using System.Collections;
using System.Collections.Generic;

class Geeks {

    // Main Method
    public static void Main(String[] args)
    {

        // Creating an List<T> of Integers
        List<int> firstlist = new List<int>();

        // Adding elements to List
        firstlist.Add(17);
        firstlist.Add(19);
        firstlist.Add(21);
        firstlist.Add(9);
        firstlist.Add(75);
        firstlist.Add(19);
        firstlist.Add(73);

        Console.WriteLine("Elements Present in List:\n");

        int p = 0;

        // Displaying the elements of List
        foreach(int k in firstlist)
        {
            Console.Write("At Position {0}: ", p);
            Console.WriteLine(k);
            p++;
        }

        Console.WriteLine(" ");

        // removing the element at index 3
        Console.WriteLine("Removing the element at index 3\n");

        // taking negative index
        // it will give error as index
        // cannot be less than 0
        firstlist.RemoveAt(-1);

        int p1 = 0;

        // Displaying the elements of List
        foreach(int n in firstlist)
        {
            Console.Write("At Position {0}: ", p1);
            Console.WriteLine(n);
            p1++;
        }
    }
}

Runtime Error:

Unhandled Exception:
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

Output:

Elements Present in List:

At Position 0: 17
At Position 1: 19
At Position 2: 21
At Position 3: 9
At Position 4: 75
At Position 5: 19
At Position 6: 73
 
Removing the element at index 3

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1.removeat?view=netframework-4.7.2