C# | Remove entry with specified key from OrderedDictionary

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

Syntax:

public void Remove (object key);

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

Exceptions:

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

Below given are some examples to understand the implementation in a better way:

Example 1:

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

class GFG {

    // Driver method
    public static void Main()
    {

        // Creating a orderedDictionary named myDict
        OrderedDictionary myDict = new OrderedDictionary();

        // Adding key and value in myDict
        myDict.Add("key1", "value1");
        myDict.Add("key2", "value2");
        myDict.Add("key3", "value3");
        myDict.Add("key4", "value4");
        myDict.Add("key5", "value5");

        // Displaying the number of element initially
        Console.WriteLine("Number of elements are : "
                                     + myDict.Count);

        // Displaying the elements in myDict
        foreach(DictionaryEntry de in myDict)
            Console.WriteLine(de.Key + " -- " + de.Value);

        // Removing the entry with the specified
        // key from the OrderedDictionary
        myDict.Remove("key2");

        // Displaying the number of element initially
        Console.WriteLine("Number of elements are : "
                                     + myDict.Count);

        // Displaying the elements in myDict
        foreach(DictionaryEntry de in myDict)
            Console.WriteLine(de.Key + " -- " + de.Value);
    }
}

Output:

Number of elements are : 5
key1 -- value1
key2 -- value2
key3 -- value3
key4 -- value4
key5 -- value5
Number of elements are : 4
key1 -- value1
key3 -- value3
key4 -- value4
key5 -- value5

Example 2:

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

class GFG {

    // Driver method
    public static void Main()
    {

        // Creating a orderedDictionary named myDict
        OrderedDictionary myDict = new OrderedDictionary();

        // Adding key and value in myDict
        myDict.Add("A", "Apple");
        myDict.Add("B", "Banana");
        myDict.Add("C", "Cat");
        myDict.Add("D", "Dog");

        // Displaying the number of element initially
        Console.WriteLine("Number of elements are : "
                                     + myDict.Count);

        // Displaying the elements in myDict
        foreach(DictionaryEntry de in myDict)
            Console.WriteLine(de.Key + " -- " + de.Value);

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

        // Displaying the number of element initially
        Console.WriteLine("Number of elements are : "
                                     + myDict.Count);

        // Displaying the elements in myDict
        foreach(DictionaryEntry de in myDict)
            Console.WriteLine(de.Key + " -- " + de.Value);
    }
}

Runtime Error:

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

Note:

• The entries that follow the removed entry move up to occupy the vacated spot and the indexes of the entries that get moved are also updated.
• If the OrderedDictionary collection does not contain an entry with the specified key, the OrderedDictionary remains unchanged and no exception is thrown.

Reference:

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