C# SortedList

A SortedList is a non-generic collection that contains key/value pairs where keys are sorted in an order. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create a SortedList
        SortedList myList = new SortedList();
        myList.Add(2, "Python");
        myList.Add(1, "Java");
        myList.Add(3, "C");

        // iterate through myList 
        for (int i = 0; i < myList.Count; i++)
        {
            Console.WriteLine("{0} : {1} ", myList.GetKey(i),
            myList.GetByIndex(i));
        }
    }
}

Output

1 : Java 
2 : Python 
3 : C 

Here, myList is a SortedList that contains key/value pairs.

We will learn about SortedList in detail.

Create an SortedList

To create SortedList in C#, we need to use the System.Collections namespace. Here is how we can create SortedList:

// create a sorted list 
SortedList myList = new SortedList();

Here, we have created a SortedList named myList.

Basic Operations on SortedList

In C#, we can perform different operations on sortedlist. We will look at some commonly used SortedList operations in this tutorial:

• Add Elements
• Access Elements
• Change Elements
• Remove Elements

Let's see how we can perform these operations in detail!

Add Elements in SortedList

C# provides a method Add() using which we can add elements in SortedList. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create a SortedList and add items 
        SortedList person = new SortedList();
 
        person.Add(2, 45);
        person.Add(1, "Jack");
        person.Add(3, "Florida");
    }
}

In the above example, we have created a SortedList named person.

Then we added three values, one integer type(45) and two string type ("Jack" and "Florida") along with their keys(2, 1 and 3).

Access the SortedList

We can access the elements inside the SortedList using it's keys. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        SortedList myList = new SortedList();
        myList.Add(2, "Python");
        myList.Add(1, "Java");
        myList.Add(3, "C");

        // access the element whose key is 2
        Console.WriteLine("Element whose key is 2: " + myList[2]);

        // access the element whose key is 1
        Console.WriteLine("Element whose key is 1: " + myList[1]);
    }
}

Output

Element whose key is 2: Python
Element whose key is 1: Java

In the above example, we have accessed the elements using their keys:

• myList[2] - accesses the element whose key is 2
• myList[1] - accesses the element whose key is 1

Note: While accessing, if we pass the key which does not exist, the compiler throws an error.

Iterate through SortedList

In C#, we can also loop through each element of SortedList using a for loop. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        SortedList myList = new SortedList();
        myList.Add(2, "BMW");
        myList.Add(1, 96);
        myList.Add(3, "Pizza");

        // iterate through myList 
        for (int i = 0; i < myList.Count; i++)
        {
            Console.WriteLine("{0} : {1} ", myList.GetKey(i),
            myList.GetByIndex(i));
        }
    }
}

Output

1 : 96 
2 : BMW 
3 : Pizza

In the above example, we have used a for loop to iterate through myList.

In order to get the keys and values of the SortedList, we use the GetKey() and GetByIndex() methods respectively.

Since the SortedList arranges the keys in ascending order, the output the keys are sorted.

Note: The Count property counts the total number of elements inside the list.

Remove SortedList Elements

We can delete one or more items from SortedList using 2 methods:

• Remove(key) - removes the element according to the specified key
• RemoveAt(index) - removes the element according to the specified index

Let's see examples using both methods.

Example: Remove() Method

using System;
using System.Collections;

class Program {
	public static void Main() {
	    SortedList myList = new SortedList();
	    myList.Add(2, "Evermore");
	    myList.Add(1, "Reputation");
	    myList.Add(3, "Folklore");
	    
	
   // remove element whose key is 1 i.e "Reputation" 
	    myList.Remove(1);
	    
	    // iterating through the modified SortedList
	    for (int i =0; i< myList.Count; i++) {
	        Console.WriteLine("{0} : {1} ", myList.GetKey(i), 
	        myList.GetByIndex(i));
	    }
        }
}

Output

2 : Evermore 
3 : Folklore 

In the above example, we have removed the element whose key is 1.

Here, myList.Remove(1) removes "Reputation" from myList. So when we iterate through myList we get a modified list as an output.

Example: RemoveAt() Method

using System;
using System.Collections;

class Program {
	public static void Main() {
	    SortedList myList = new SortedList();
	    myList.Add(2, "Evermore");
	    myList.Add(1, "Reputation");
	    myList.Add(3, "Folklore");
	    
	
   // remove element which is present in index 1 i.e "Evermore" 
	    myList.RemoveAt(1);
	    
	    // iterating through the modified SortedList
	    for (int i =0; i< myList.Count; i++) {
	        Console.WriteLine("{0} : {1}  ", myList.GetKey(i), 
	        myList.GetByIndex(i));
	    }
	}
}

Output

1 : Reputation  
3 : Folklore