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C# | Remove the entry with specified key from ListDictionary

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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 :

Last Updated : 01 Feb, 2019
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