C# | Remove entry with specified key from the StringDictionary - GeeksforGeeks

01 Feb, 2019
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 StringDictionaryusing 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 StringDictionaryusing 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
CSharp-Collections-Namespace
CSharp-method
CSharp-Specialized-Namespace
CSharp-Specialized-StringDictionary
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