C# | Remove the entry with specified key from ListDictionary

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

Syntax:

public void Remove (object key);

Here, key is the key of the entry which is to be removed.

Exception: This method will give ArgumentNullException if the key is null.

Below are the examples to illustrate the use of ListDictionary.Remove(Object) Method:

Example 1:

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

class GFG {

    // Driver code
    public static void Main()
    {

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

        // Adding key/value pairs in myDict
        myDict.Add("Australia", "Canberra");
        myDict.Add("Belgium", "Brussels");
        myDict.Add("Netherlands", "Amsterdam");
        myDict.Add("China", "Beijing");
        myDict.Add("Russia", "Moscow");
        myDict.Add("India", "New Delhi");

        // To get count of key/value pairs in myDict
        Console.WriteLine("Total 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);
        }

        // Remove the entry with the specified
        // key from the ListDictionary
        myDict.Remove("Russia");

        // To get count of key/value pairs in myDict
        Console.WriteLine("Total 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:

Total key/value pairs in myDict are : 6
The key/value pairs in myDict are : 
Australia Canberra
Belgium Brussels
Netherlands Amsterdam
China Beijing
Russia Moscow
India New Delhi
Total key/value pairs in myDict are : 5
The key/value pairs in myDict are : 
Australia Canberra
Belgium Brussels
Netherlands Amsterdam
China Beijing
India New Delhi

Example 2 :

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

class GFG {

    // Driver code
    public static void Main()
    {

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

        // 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");

        // To get count of key/value pairs in myDict
        Console.WriteLine("Total 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);
        }

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

        // To get count of key/value pairs in myDict
        Console.WriteLine("Total 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 ListDictionary does not contain an element with the specified key, the ListDictionary remains unchanged. No exception is thrown.
• This method is an O(n) operation, where n is Count.

Reference :

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