C# | Removing the specified key entry from HybridDictionary

Last Updated : 11 Jul, 2025

HybridDictionary.Remove(Object) method is used to remove the entry with the specified key from the HybridDictionary. Syntax:

public void Remove (object key);

Here, key is the key of the entry to remove. Exception: This method throws ArgumentNullException if the key is null. Below given are some examples to understand the implementation in a better way : Example 1:

CSHARP

// C# code to remove the entry
// with the specified key from
// the HybridDictionary.
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HybridDictionary named myDict
        HybridDictionary myDict = new HybridDictionary();

        // Adding key/value pairs in myDict
        myDict.Add("A", "Apple");
        myDict.Add("B", "Banana");
        myDict.Add("C", "Cat");
        myDict.Add("D", "Dog");
        myDict.Add("E", "Elephant");
        myDict.Add("F", "Fish");

        // Displaying the number of key/value
        // pairs in HybridDictionary myDict
        Console.WriteLine("Number of key/value pairs in myDict are : " 
                                                      + myDict.Count);

        // Displaying the key/value pairs in myDict
        Console.WriteLine("The key/value pairs in myDict are : ");

        foreach(DictionaryEntry de in myDict)
        {
            Console.WriteLine(de.Key + " --> " + de.Value);
        }

        // Removing the entry with the
        // specified key from the HybridDictionary.
        myDict.Remove("C");

        // Displaying the number of key/value
        // pairs in HybridDictionary myDict
        Console.WriteLine("Number of key/value pairs in myDict are : " 
                                                      + myDict.Count);

        // Displaying the key/value pairs in myDict
        Console.WriteLine("The key/value pairs in myDict are : ");

        foreach(DictionaryEntry de in myDict)
        {
            Console.WriteLine(de.Key + " --> " + de.Value);
        }
    }
}

Output:

Number of key/value pairs in myDict are : 6
The key/value pairs in myDict are : 
A --> Apple
B --> Banana
C --> Cat
D --> Dog
E --> Elephant
F --> Fish
Number of key/value pairs in myDict are : 5
The key/value pairs in myDict are : 
A --> Apple
B --> Banana
D --> Dog
E --> Elephant
F --> Fish

Example 2:

CSHARP

// C# code to remove the entry
// with the specified key from
// the HybridDictionary.
using System;
using System.Collections;
using System.Collections.Specialized;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HybridDictionary named myDict
        HybridDictionary myDict = new HybridDictionary();

        // Adding key/value pairs in myDict
        myDict.Add("I", "first");
        myDict.Add("II", "second");
        myDict.Add("III", "third");
        myDict.Add("IV", "fourth");
        myDict.Add("V", "fifth");

        // Displaying the number of key/value
        // pairs in HybridDictionary myDict
        Console.WriteLine("Number of key/value pairs in myDict are : "
                                                      + myDict.Count);

        // Displaying the key/value pairs in myDict
        Console.WriteLine("The key/value pairs in myDict are : ");

        foreach(DictionaryEntry de in myDict)
        {
            Console.WriteLine(de.Key + " --> " + de.Value);
        }

        // Removing the entry with the
        // specified key from the HybridDictionary.
        // This should raise "ArgumentNullException"
        // as the key is "null"
        myDict.Remove(null);

        // Displaying the number of key/value
        // pairs in HybridDictionary myDict
        Console.WriteLine("Number of key/value pairs in myDict are : " 
                                                      + myDict.Count);

        // Displaying the key/value pairs in myDict
        Console.WriteLine("The key/value pairs in myDict are : ");

        foreach(DictionaryEntry de in myDict)
        {
            Console.WriteLine(de.Key + " --> " + de.Value);
        }
    }
}

Runtime Error:

Unhandled Exception: System.ArgumentNullException: Key cannot be null. Parameter name: key

Note:

If the HybridDictionary does not contain an element with the specified key, the HybridDictionary remains unchanged. No exception is thrown.
If the collection is already stored in a Hashtable and the number of elements falls below the optimal size for a ListDictionary, the collection remains in the Hashtable to avoid the overhead of copying elements from the Hashtable back to a ListDictionary.
This method is an O(1) operation.

Reference:

https://learn.microsoft.com/en-us/dotnet/api/system.collections.specialized.hybriddictionary.remove?view=netframework-4.7.2

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