C# | Remove entry with specified key from the StringDictionary

StringDictionary.Remove(String) method is used to remove the entry with the specified key from the string dictionary.

Syntax:

public virtual void Remove (string key);

Here, key is the key of the entry to remove.

Exceptions:

• ArgumentNullException: If the key is null.
• NotSupportedException: If the StringDictionary is read-only.

Below programs illustrate the use of StringDictionary.Remove(String) method:

Example 1:

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

class GFG {

    // Driver code
    public static void Main()
    {

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

        // Adding key and value into the StringDictionary
        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 keys and values in StringDictionary
        Console.WriteLine("The number of key/value pairs are : " + myDict.Count);

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

        // Removing the entry with the specified
        // key from the StringDictionary
        myDict.Remove("D");

        // Displaying the keys and values in StringDictionary
        Console.WriteLine("The number of key/value pairs are : " + myDict.Count);

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

Output:

The number of key/value pairs are : 6
b Banana
c Cat
a Apple
f Fish
d Dog
e Elephant
The number of key/value pairs are : 5
b Banana
c Cat
a Apple
f Fish
e Elephant

Example 2:

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

class GFG {

    // Driver code
    public static void Main()
    {

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

        // Adding key and value into the StringDictionary
        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 keys and values in StringDictionary
        Console.WriteLine("The number of key/value pairs are : " + myDict.Count);

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

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

        // Displaying the keys and values in StringDictionary
        Console.WriteLine("The number of key/value pairs are : " + myDict.Count);

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

Runtime Error:

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

Note:

• If the StringDictionary does not contain an element with the specified key, the StringDictionary remains unchanged. No exception is thrown.
• The key is handled in a case-insensitive manner, i.e, it is translated to lowercase before it is used to find the entry to remove from the StringDictionary.
• This method is an O(1) operation.

Reference:

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