C# OrderedDictionary Class
Last Updated : 04 Feb, 2025
In C#, the OrderedDictionary Class represents a collection of key/value pairs that are accessible by the key or index. It is present in System.Collections.Specialized namespace.
- It implements both IDicitonary and ICollection interfaces.
- Allows indexed access to elements via both keys and numeric indexes.
- It provides the ability to iterate over the elements while maintaining the order of insertion.
Example: This example demonstrates how to use the OrderedDictionary class to store and iterate over key-value pairs while maintaining the order in which the elements are added.
C# // C# program to demonstrates the // working of OrderedDictionary using System; using System.Collections.Specialized; using System.Collections; class Geeks { static void Main() { // Create an OrderedDictionary instance OrderedDictionary od = new OrderedDictionary(); // Add key-value pairs od.Add("Geek1", 1); od.Add("Geek2", 2); od.Add("Geek3", 3); od.Add("Geek4", 4); // Iterate through the OrderedDictionary // and print the key-value pairs foreach (DictionaryEntry i in od) { Console.WriteLine($"{i.Key}: {i.Value}"); } } } OutputGeek1: 1 Geek2: 2 Geek3: 3 Geek4: 4
Declaration of OrderedDictionary
In C#, the orderedDicitonary class is represented as:
OrderedDictionary orderedDict = new OrderedDictionary();
Constructors
| Constructors | Description |
|---|
| OrderedDictionary() | Initializes a new instance of the OrderedDictionary class. |
| OrderedDictionary(IEqualityComparer) | Initializes a new instance of the OrderedDictionary class using the specified comparer. |
| OrderedDictionary(Int32) | Initializes a new instance of the OrderedDictionary class using the specified initial capacity. |
| OrderedDictionary(Int32, IEqualityComparer) | Initializes a new instance of the OrderedDictionary class using the specified initial capacity and comparer. |
| OrderedDictionary(SerializationInfo, StreamingContext) | Initializes a new instance of the OrderedDictionary class that is serializable using the specified SerializationInfo and StreamingContext objects. |
Example: This example demonstrates how to create an OrderedDictionary, add key-vlaue pairs and display the count and key-value while maintaining the insertion order.
C# // C# program to demosntrate the count and // key-value pair of OrderedDictionary using System; using System.Collections; using System.Collections.Specialized; class Geeks { // Driver method public static void Main() { // Creating a orderedDictionary named myDict OrderedDictionary od = new OrderedDictionary(); // Adding key and value in myDict od.Add("1", "ONE"); od.Add("2", "TWO"); od.Add("3", "THREE"); // Displaying the number of key/value // pairs in myDict Console.WriteLine("The count is : " + od.Count); // Displaying the key/value pairs in myDict foreach(DictionaryEntry i in od) Console.WriteLine(i.Key + " --> " + i.Value); } } OutputThe count is : 3 1 --> ONE 2 --> TWO 3 --> THREE
Properties
The OrderedDictionary class provides several properties to access its state.
| Properties | Description |
|---|
| Count | Gets the number of key/values pairs contained in the OrderedDictionary collection. |
| IsReadOnly | Gets a value indicating whether the OrderedDictionary collection is read-only. |
| Item[Int32] | Gets or sets the value at the specified index. |
| Item[Object] | Gets or sets the value with the specified key. |
| Keys | Gets an ICollection object containing the keys in the OrderedDictionary collection. |
| Values | Gets an ICollection object containing the values in the OrderedDictionary collection. |
Example 1: This example checks if the dictionary is read-only using the IsReadOnly property.
C# // C# code to check if OrderedDictionary // collection is read-only using System; using System.Collections; using System.Collections.Specialized; class Geeks { public static void Main() { // Creating a orderedDictionary named myDict OrderedDictionary od = new OrderedDictionary(); // Adding key and value in myDict od.Add("key1", "value1"); od.Add("key2", "value2"); od.Add("key3", "value3"); // Checking if OrderedDictionary // collection is read-only Console.WriteLine(od.IsReadOnly); } } Example 2: This example demonstrates the count of key-value pairs using the Count property.
C# // C# code to get the number of // key/values pairs contained // in the OrderedDictionary using System; using System.Collections; using System.Collections.Specialized; class Geeks { public static void Main() { // Creating a orderedDictionary named myDict OrderedDictionary od = new OrderedDictionary(); // Adding key and value in myDict od.Add("1", "Geeks"); od.Add("2", "for"); od.Add("3", "Geeks"); od.Add("4", "C#"); // To Get the number of key/values // pairs contained in the OrderedDictionary Console.WriteLine("Number of key-value pairs are : " + od.Count); } } OutputNumber of key-value pairs are : 4
Methods
| Methods | Description |
|---|
| Add(Object, Object) | Adds an entry with the specified key and value into the OrderedDictionary collection with the lowest available index. |
| AsReadOnly() | Returns a read-only copy of the current OrderedDictionary collection. |
| Clear() | Removes all elements from the OrderedDictionary collection. |
| Contains(Object) | Determines whether the OrderedDictionary collection contains a specific key. |
| CopyTo(Array, Int32) | Copies the OrderedDictionary elements to a one-dimensional Array object at the specified index. |
| Equals(Object) | Determines whether the specified object is equal to the current object. |
| GetEnumerator() | Returns an IDictionaryEnumerator object that iterates through the OrderedDictionary collection. |
| GetHashCode() | Serves as the default hash function. |
| GetObjectData(SerializationInfo, StreamingContext) | Implements the ISerializable interface and returns the data needed to serialize the OrderedDictionary collection. |
| GetType() | Gets the Type of the current instance. |
| Insert(Int32, Object, Object) | Inserts a new entry into the OrderedDictionary collection with the specified key and value at the specified index. |
| MemberwiseClone() | Creates a shallow copy of the current Object. |
| OnDeserialization(Object) | Implements the ISerializable interface and is called back by the deserialization event when deserialization is complete. |
| Remove(Object) | Removes the entry with the specified key from the OrderedDictionary collection. |
| RemoveAt(Int32) | Removes the entry at the specified index from the OrderedDictionary collection. |
| ToString() | Returns a string that represents the current object. |
Example 1: This example demonstrates how to create an OrderedDictionary, add key-value pairs and obtain a read-only copy of the docitonatry using AsReadOnly().
C# // C# code to get a read-only // copy of the OrderedDictionary using System; using System.Collections; using System.Collections.Specialized; class Geeks { public static void Main() { // Creating a orderedDictionary named myDict OrderedDictionary od = new OrderedDictionary(); // Adding key and value in myDict od.Add("key1", "value1"); od.Add("key2", "value2"); od.Add("key3", "value3"); // To Get a read-only copy of // the OrderedDictionary OrderedDictionary d = od.AsReadOnly(); // Checking if d is read-only Console.WriteLine(d.IsReadOnly); } } Example 2: This example demonstrates, how to remove an entry and display the updated count and elements.
C# // C# code to remove the entry // with the specified key from // the OrderedDictionary using System; using System.Collections; using System.Collections.Specialized; class Geeks { public static void Main() { // Creating a orderedDictionary named myDict OrderedDictionary od = new OrderedDictionary(); // Adding key and value in myDict od.Add("key1", "value1"); od.Add("key2", "value2"); od.Add("key3", "value3"); // Displaying the number of element initially Console.WriteLine("Number of elements are : " + od.Count); // Displaying the elements in myDict foreach(DictionaryEntry i in od) Console.WriteLine(i.Key + " --> " + i.Value); // Removing the entry with the specified // key from the OrderedDictionary od.Remove("key2"); // Displaying the number of element initially Console.WriteLine("Number of elements are: " + od.Count); // Displaying the elements in myDict foreach(DictionaryEntry i in od) Console.WriteLine(i.Key + " -->" + i.Value); } } OutputNumber of elements are : 3 key1 --> value1 key2 --> value2 key3 --> value3 Number of elements are: 2 key1 -->value1 key3 -->value3
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