C# SortedDictionary Class

Last Updated : 03 Feb, 2025

In C#, the SortedDictionary<TKey,TValue> class represents the collection of key/value pairs. This pair is in sorted form and the sorting is done on the key. This class is defined under System.Collections.Generic namespace.

In the SortedDictionary class, the keys are immutable, always unique, and cannot be null. We are allowed to use null in value if the type of value is of reference type.
The SortedDictionary class provides the fastest insertion and removal operations for unsorted data.
The key/value pair of the SortedDictionary class is retrieved by using the KeyValuePair structure.

Example: This example, demonstrates how to create a SortedDictionary, insert key-value pairs, and iterate through it to display the sorted key-value pairs.

// C# Program to add elements in a SortedDictionary
using System;
using System.Collections.Generic;

class Geeks {
    static void Main()
    {
        // Create a SortedDictionary to store key-value
        // pairs
        SortedDictionary<string, int> sd
            = new SortedDictionary<string, int>();

        // Insert elements into the SortedDictionary
        sd.Add("Geek1", 1);
        sd.Add("Geek2", 2);
        sd.Add("Geek3", 3);

        // Display all key-value pairs in the
        // SortedDictionary
        foreach(var i in sd)
        {
            Console.WriteLine(
                $"key: {i.Key}, value: {i.Value}");
        }
    }
}

Output

key: Geek1, value: 1
key: Geek2, value: 2
key: Geek3, value: 3

Declarartion of SortedDictionary

In C#, the declaration of SortedDictionary can be done as:

SortedDictionary<TKey, TValue> dictionaryName;

Parameters:

TKey: Denotes the type of the keys in the dictionary.
TValue: Denotes the type of the value in the dictionary.

Constructors

Constructors	Description
SortedDictionary<TKey,TValue>()	Initializes a new instance of the SortedDictionary class that is empty and uses the default IComparer implementation for the key type.
SortedDictionary<TKey,TValue>(IComparer)	Initializes a new instance of the SortedDictionary class that is empty and uses the specified IComparer implementation to compare keys.
SortedDictionary<TKey,TValue>(IDictionary)	Initializes a new instance of the SortedDictionary class that contains elements copied from the specified IDictionary and uses the default IComparer implementation for the key type.
SortedDictionary<TKey,TValue>(IDictionary, IComparer)	Initializes a new instance of the SortedDictionary class that contains elements copied from the specified IDictionary and uses the specified IComparer implementation to compare keys.

Example: This example demonstrates how to create a Sortedlist, add elements and iterate over the elements where the keys are integer and values are string.

// C# program to demonstrate the 
// concept of SortedDictionary
using System;
using System.Collections.Generic;

public class Geeks {

    static public void Main()
    {

        // Create a new SortedDictionary 
        // of strings, with int keys 
        SortedDictionary<int, string> sd =
                new SortedDictionary<int, string>();

        // Adding key/value pairs 
        sd.Add(1, "C");
        sd.Add(2, "C++");
        sd.Add(3, "C#");

        // Display the key/value pairs 
        foreach(KeyValuePair<int, string> pair in sd)
        {
            Console.WriteLine("Key: {0} and Value: {1}",
                    pair.Key, pair.Value);
        }
    }
}

Output

Key: 1 and Value: C
Key: 2 and Value: C++
Key: 3 and Value: C#

Properties

Properties	Description
Comparer	Gets the IComparer used to order the elements of the SortedDictionary.
Count	Gets the number of key/value pairs contained in the SortedDictionary.
Item[TKey]	Gets or sets the value associated with the specified key.
Keys	Gets a collection containing the keys in the SortedDictionary.
Values	Gets a collection containing the values in the SortedDictionary.

Example: This example demonstrates how to use the Count property.

// C# program to demonstrates the concept 
// of Count property in SortedDictionary 
using System;
using System.Collections.Generic;

public class Geeks {

    static public void Main()
    {

        // Create a new SortedDictionary 
        // of strings, with int keys 
        SortedDictionary<int, string> sd =
                new SortedDictionary<int, string>();

        // Adding key/value pairs 
        sd.Add(1, "Geek1");
        sd.Add(2, "Geek2");
        sd.Add(3, "Geek3");
        sd.Add(4, "Geek4");

        // Display the total number of 
        // key/value pairs present
        Console.WriteLine("Total number of pairs "+
                "present in SortedDictionary : {0}", sd.Count);
    }
}

Output

Total number of pairs present in SortedDictionary : 4

Methods

Methods	Description
Add(TKey, TValue)	Adds an element with the specified key and value into the SortedDictionary.
Clear()	Removes all elements from the SortedDictionary.
ContainsKey(TKey)	Determines whether the SortedDictionary contains an element with the specified key.
ContainsValue(TValue)	Determines whether the SortedDictionary contains an element with the specified value.
CopyTo(KeyValuePair<TKey,TValue>[], Int32)	Copies the elements of the SortedDictionary to the specified array of KeyValuePair structures, starting at the specified index.
Equals(Object)	Determines whether the specified object is equal to the current object.
GetEnumerator()	Returns an enumerator that iterates through the SortedDictionary.
GetHashCode()	Serves as the default hash function.
GetType()	Gets the Type of the current instance.
MemberwiseClone()	Creates a shallow copy of the current Object.
Remove(TKey)	Removes the element with the specified key from the SortedDictionary.
ToString()	Returns a string that represents the current object.
TryGetValue(TKey, TValue)	Gets the value associated with the specified key.

Example: This example demonstrates how to remove key-value pair from a SortedDictionary.

// C# program to demonstrates how
// to remove elements in SortedDictionary
using System;
using System.Collections.Generic;

public class Geeks {
    static public void Main()
    {
        // Create a new SortedDictionary of int keys and
        // string values
        SortedDictionary<int, string> sd
            = new SortedDictionary<int, string>();

        // Adding key/value pairs to the SortedDictionary
        sd.Add(1, "Geek1");
        sd.Add(2, "Geek2");
        sd.Add(3, "Geek3");


        // Display the SortedDictionary before removal
        Console.WriteLine(
            "SortedDictionary before removal:");
        foreach(KeyValuePair<int, string> pair in sd)
        {
            Console.WriteLine("Key: {0}, Value: {1}",
                              pair.Key, pair.Value);
        }

        // Remove an element from the SortedDictionary
        sd.Remove(2);

        // Display the SortedDictionary after removal
        Console.WriteLine(
            "\nSortedDictionary after removal:");
        foreach(KeyValuePair<int, string> pair in sd)
        {
            Console.WriteLine("Key: {0}, Value: {1}",
                              pair.Key, pair.Value);
        }
    }
}

Output

SortedDictionary before removal:
Key: 1, Value: Geek1
Key: 2, Value: Geek2
Key: 3, Value: Geek3

SortedDictionary after removal:
Key: 1, Value: Geek1
Key: 3, Value: Geek3