C# | Remove the element at the specified index of the ArrayList

ArrayList represents an ordered collection of an object that can be indexed individually. It is basically an alternative to an array. It also allows dynamic memory allocation, adding, searching and sorting items in the list. ArrayList.RemoveAt(Int32) method is used to remove the element at the specified index of the ArrayList.

Properties:

• Elements can be added or removed from the Array List collection at any point in time.
• The ArrayList is not guaranteed to be sorted.
• The capacity of an ArrayList is the number of elements the ArrayList can hold.
• Elements in this collection can be accessed using an integer index. Indexes in this collection are zero-based.
• It also allows duplicate elements.
• Using multidimensional arrays as elements in an ArrayList collection is not supported.

Syntax:

public virtual void RemoveAt (int index);

Here, index is the zero-based index of the element to remove.

Exceptions:

• ArgumentOutOfRangeException: If index is less than zero or index is equal to or greater than Count, where Count is number of elements in ArrayList.
• NotSupportedException: If the ArrayList is read-only or the ArrayList has a fixed size.

Below given are some examples to understand the implementation in a better way:

Example 1:

// C# code to remove the element at
// the specified index of ArrayList
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList(10);

        // Adding elements to ArrayList
        myList.Add("A");
        myList.Add("B");
        myList.Add("C");
        myList.Add("D");
        myList.Add("E");
        myList.Add("F");

        // Displaying the elements in ArrayList
        Console.WriteLine("The elements in ArrayList initially are :");

        foreach(string str in myList)
            Console.WriteLine(str);

        // Removing the element present at index 4
        myList.RemoveAt(4);

        // Displaying the elements in ArrayList
        Console.WriteLine("The elements in ArrayList are :");

        foreach(string str in myList)
            Console.WriteLine(str);
    }
}

Output:

The elements in ArrayList initially are:
A
B
C
D
E
F
The elements in ArrayList are:
A
B
C
D
F

Example 2:

// C# code to remove the element at
// the specified index of ArrayList
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList(10);

        // Adding elements to ArrayList
        myList.Add(2);
        myList.Add(3);
        myList.Add(4);
        myList.Add(5);
        myList.Add(6);
        myList.Add(7);

        // Removing the element present at index 7
        // It should raise System.ArgumentOutOfRangeException
        myList.RemoveAt(7);

        // Displaying the elements in ArrayList
        Console.WriteLine("The elements in ArrayList are :");

        foreach(int i in myList)
            Console.WriteLine(i);
    }
}

Output:

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

Note:

• This method is an O(n) operation, where n is Count.
• After the element is removed, the size of the collection is adjusted and the value of the Count property is decreased by one.

Reference:

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