C# | Remove the first occurrence of a specific object from 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.Remove(Object) method is used to remove the first occurrence of a specific object from 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 Remove (object obj);

Here, obj is the Object to remove from the ArrayList. The value can be null.

Exceptions: This method will give NotSupportedException if the ArrayList is read-only or has a fixed size.

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

Example 1:

// C# code to remove the first
// occurrence of a specific
// object from the 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("C");
        myList.Add("C#");
        myList.Add("Java");
        myList.Add("C#");
        myList.Add("PHP");
        myList.Add("C#");

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

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

        // Removing the first
        // occurrence of C#
        myList.Remove("C#");

        // 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 :
C
C#
Java
C#
PHP
C#
The elements in ArrayList are :
C
Java
C#
PHP
C#

Example 2:

// C# code to remove the first
// occurrence of a specific
// object from the 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("Geeks");
        myList.Add("Noida");
        myList.Add("Classes");
        myList.Add("GFG");
        myList.Add("DS");
        myList.Add("Algorithms");

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

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

        // Removing the first
        // occurrence of HTML
        // As HTML is not present so
        // it return the ArrayList as it is
        myList.Remove("HTML");

        // 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 :
Geeks
Noida
Classes
GFG
DS
Algorithms
The elements in ArrayList are :
Geeks
Noida
Classes
GFG
DS
Algorithms

Note:

• This method performs a linear search, therefore, this method is an O(n) operation, where n is Count.
• If the ArrayList does not contain the specified object, the ArrayList remains unchanged. No exception is thrown.

Reference:

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