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C# SortedList - GeeksforGeeks

C# SortedList

Last Updated : 11 Jul, 2025

In C#, SortedList is a collection of key-value pairs sorted according to keys. By default, this collection sorts ascendingly It is of both generic and non-generic type of collection. The generic SortedList is defined in the System.Collections.Generic namespace whereas non-generic SortedList is defined under System.Collections namespace, here we will discuss the non-generic type SortedList.

Elements are sorted by key in ascending order.
The keys are defined uniquely but we can store duplicate values.
Offer to store data in keys and value pairs.
No need to define the size we can add elements without giving the size like arrays.

Example:


 // Creating and adding key, values to the sorted list
using System;
using System.Collections.Generic;

class Geeks
{
    public static void Main()
    {
        // Creating a SortedList
        SortedList<int, string> sl = new SortedList<int, string>();

        // Adding key-value pairs
        sl.Add(3, "Three");
        sl.Add(1, "One");
        sl.Add(2, "Two");

        // Displaying elements in sorted by key
        foreach (var item in sl)
        {
            Console.WriteLine($"Key: {item.Key}, Value: {item.Value}");
        }
    }
}

Output

Key: 1, Value: One
Key: 2, Value: Two
Key: 3, Value: Three

Steps to Create SortedList

We can use the SortedList Class which provides different ways to create a Sorted list. Here, we use the SortedList Class constructor to create a sorted list. Which is used to create an instance of the SortedList class that is empty by default and sorted according to the IComparable interface implemented by each key added to the SortedList object.

Step 1: Include System.Collections namespace

using System.Collections;

Step 2: Create a SortedList using the SortedList class

SortedList list_name = new SortedList();

Performing Different Operations on SortedList 1. Adding Elements

For adding elements list, The List<T> class provides two different methods which are:

Add() : This method is used to add an object to the SortedList<T>.
Collection Initializer: We can use Collection Initializer to add elements in SortedList<TKey, TValue>.

Syntax:

// Add element using Add method
list.Add(key, value);

// Adding elements using the
// Collection initializers
SortedList<Tkey, Tvalue> mySortedList = new SortedList<int, string>()

{
{ Key, Value },
{ Key, Value },
};

Example: Creating sortedList using different ways.


 // C# program to illustrate how
// to create a sortedlist
using System;
using System.Collections;

class Geeks {
static public void Main() {
  
		// Creating a sortedlist
		// Using SortedList class
		SortedList sl = new SortedList();

		// Adding key-value pairs in 
		// SortedList using Add() method
		sl.Add(1.02, "This");
		sl.Add(1.07, "Is");
		sl.Add(1.04, "SortedList");

		foreach(DictionaryEntry pair in sl)
		{
			Console.WriteLine("{0} and {1}", 
			pair.Key, pair.Value);
		}
		Console.WriteLine();

		// Creating another SortedList
		// using Object Initializer Syntax
		// to initialize sortedlist
		SortedList my_slist2 = new SortedList() {
								{ "b.09", 234 },
								{ "b.11", 395 },
								{ "b.01", 405 },
								{ "b.67", 100 }};
				
		foreach(DictionaryEntry pair in my_slist2)
		{
			Console.WriteLine("{0} and {1}", 
			pair.Key, pair.Value);
		}
	}
}

Output

1.02 and This
1.04 and SortedList
1.07 and Is

b.01 and 405
b.09 and 234
b.11 and 395
b.67 and 100

2. Accessing SortedList

There are three different ways to access the elements of the SortedList as it is stored in the Key-Value pair we can get the Key and value separately.

Using for Loop: We can use Loop to iterate through the list and access key-value pairs we can use List.GetKey() method to access the key and similarly from the key we can access the value by using List.GetByIndex(key).

Syntax:

for (int i = 0; i < sList.Count; i++)

{
Console.WriteLine("{0} and {1}",
sList.GetKey(i), // Acessing keys
sLIst.GetByIndex(i)); // Acessing values
}

Using ForEach Loop: We can use a foreach loop to access the key-value pairs of the SortedList. In the foreach loop, we can use a dictionary. It is mostly used to access the list stored in key-value pairs.

Syntax:

foreach(DictionaryEntry pair in my_slist1)
{
Console.WriteLine("{0} and {1}",
pair.Key, pair.Value);
}

Using Indexers: We can access the individual value of the SortedList by using the index. We need to pass the key or index as a parameter to find the respective value. It is similar to how we access the array.

Syntax:

Console.WriteLine("Value is:{0}", my_slist1[1.04]);
string x = (string)my_slist[1.02];
Console.WriteLine(x);

Note: If the specified key is not available, then the compiler will throw an error.

Example: Demonstration of accessing SortedList in different ways.


 // Creating a SortedList and
// accessing its elements
using System;
using System.Collections;

class Geeks
{
    static void Main()
    {
        SortedList sl = new SortedList {
        { 1, "Geek1" }, { 2, "Geek2" }, { 3, "Geek3" }
        };

        // Using for loop
        Console.WriteLine("Access using for loop");
        for (int i = 0; i < sl.Count; i++)
            Console.WriteLine($"{sl.GetKey(i)}: {sl.GetByIndex(i)}");
        

        // Using foreach loop
        Console.WriteLine("Access using foreach loop");
      
        foreach (DictionaryEntry entry in sl)
            Console.WriteLine($"{entry.Key}: {entry.Value}");
        
        // Using indexer
        Console.WriteLine("Access using indexer");
        Console.WriteLine($"Key 2: {sl[2]}" );
    }
}

Output

Access using for loop
1: Geek1
2: Geek2
3: Geek3
Access using foreach loop
1: Geek1
2: Geek2
3: Geek3
Access using indexer
Key 2: Geek2

3. Removing Elements

Clear: This method is used to remove all elements from a SortedList object.
Remove: This method is used to remove the element with the specified key from a SortedList object.
RemoveAt: This method is used to remove the element at the specified index of a SortedList object.

Example:


 // Removing key-value pairs from 
// the sortedlist
using System;
using System.Collections;

class Geeks
{
    static public void Main()
    {
        // Creating a sortedlist
        // Using SortedList class
        SortedList sl = new SortedList();

        // Adding key/value pairs in SortedList
        // Using Add() method
        sl.Add(1, "one");
        sl.Add(2, "two");
        sl.Add(3, "three");

        foreach(DictionaryEntry pair in sl)
        {
            Console.WriteLine("{0} and {1}",
                    pair.Key, pair.Value);
        }
        Console.WriteLine();

        // Remove value having 1.07 key
        // Using Remove() method
        sl.Remove(1);

        // After Remove() method
        foreach(DictionaryEntry pair in sl)
        {
            Console.WriteLine("{0} and {1}",
            pair.Key, pair.Value);
        }
        Console.WriteLine();

        // Remove element at index 2
        // Using RemoveAt() method
        sl.RemoveAt(1);

        // After RemoveAt() method
        foreach(DictionaryEntry pair in sl)
        {
            Console.WriteLine("{0} and {1}",
            pair.Key, pair.Value);
        }
        Console.WriteLine();

        // Remove all key/value pairs
        // Using Clear method
        sl.Clear();
        Console.WriteLine("Total pairs"+
        " present in sorted list is: {0}", sl.Count);
    }
}

Output

1 and one
2 and two
3 and three

2 and two
3 and three

2 and two

Total pairs present in sorted list is: 0

4. Check Element

We can check the element of the SortedList by using the methods available below it returns value in boolean if the the element present returns true either false.

Contains: This method is used to check whether a SortedList object contains a specific.
ContainsKey: This method is used to check whether a SortedList object contains a specific key.
ContainsValue: This method is used to check whether a SortedList object contains a specific value.

Example:


 // Check the given key or value 
// present in the sortedlist or not
using System;
using System.Collections;

class Geeks
{
    static public void Main()
    {
        // Creating a sortedlist
        // Using SortedList class
        SortedList sl = new SortedList();

        // Adding key-value pairs in 
        // SortedList using Add() method
        sl.Add(1, "one");
        sl.Add(2, "two");
        sl.Add(3, "three");

        // Using Contains() method to check
        // the specified key is present or not
        if (sl.Contains(1))
            Console.WriteLine("Key is found...!!");

        else
            Console.WriteLine("Key is not found...!!");


        // Using ContainsKey() method to check
        // the specified key is present or not
        if (sl.ContainsKey(2))
            Console.WriteLine("Key is found...!!");
        else
            Console.WriteLine("Key is not found...!!");

        // Using ContainsValue() method to check
        // the specified value is present or not
        if (sl.ContainsValue("one"))
            Console.WriteLine("Value is found...!!");

        else
            Console.WriteLine("Value is not found...!!");
    }
}

Output

Key is found...!!
Key is found...!!
Value is found...!!

Important Points

The SortedList class implements the IEnumerable, ICollection, IDictionary and ICloneable interfaces.
In SortedList, an element can be accessed by its key or by its index.
A SortedList object internally maintains two arrays to store the elements of the list, i.e., one array for the keys and another for the associated values.
Here, a key cannot be null, but a value can be.
The capacity of a SortedList object is the number of key-value pairs it can hold.
In SortedList, duplicate keys are not allowed.
In SortedList, we can store values of the same type and of the different types due to the non-generic collection. If you use a generic SortedList in your program, then the type of the values must be the same.
SortedList only allows keys of the same type, mixing types will cause a compiler exception.
We can also cast key/value pair of SortedList into DictionaryEntry.

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