C# SortedList Tutorial with Examples

SortedList in C# combines features of arrays and hashtables, storing key-value pairs in sorted order by keys. Here's what you need to know:

• Maintains elements in sorted order automatically
• Allows lookups by key and index
• Useful for scenarios needing constant sorting and fast access
• Balances features of List and Dictionary

Key features:

• Unique, non-null keys
• Null or duplicate values allowed
• Automatic sorting on insertion
• Key and index-based access

Quick comparison:

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SortedList basics

SortedList stores key-value pairs sorted by keys using two internal arrays:

1. Keys array
2. Corresponding values array

SortedList<int, string> numberNames = new SortedList<int, string>();
numberNames.Add(3, "Three");
numberNames.Add(1, "One");
numberNames.Add(2, "Two");

// Keys are now sorted: 1, 2, 3

Key points:

• Unique, non-null keys
• Null or duplicate values allowed
• Automatic sorting on insertion
• Key and index-based access

SortedList shines when you need:

1. Quick lookups by key and index
2. Constantly sorted collection
3. Memory efficiency (vs SortedDictionary)

// Simple inventory system example
SortedList<string, int> inventory = new SortedList<string, int>();
inventory.Add("Apple", 50);
inventory.Add("Banana", 30);
inventory.Add("Orange", 40);

Console.WriteLine($"Apples in stock: {inventory["Apple"]}");
Console.WriteLine($"Second item: {inventory.Keys[1]} - {inventory.Values[1]}");

Making a SortedList

Create a SortedList:

using System.Collections.Generic;

// Generic SortedList
SortedList<TKey, TValue> myGenericList = new SortedList<TKey, TValue>();

// With initial values
SortedList<int, string> numberNames = new SortedList<int, string>()
{
    {3, "Three"},
    {1, "One"},
    {2, "Two"}
};

Remember:

• Keys must be unique and non-null
• Values can be null or duplicate
• Automatic sorting by key
• Set initial capacity: new SortedList<TKey, TValue>(capacity)

Adding items to SortedList

Use the Add() method:

SortedList<int, string> numberNames = new SortedList<int, string>();
numberNames.Add(3, "Three");
numberNames.Add(1, "One");
numberNames.Add(2, "Two");
numberNames.Add(4, null);

For duplicate keys, use the key indexer:

planets[3] = "Earth - Updated"; // Updates existing value
planets[4] = "Mars"; // Adds new key-value pair

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Getting items from SortedList

Retrieve items:

Console.WriteLine(numberNames[1]); // Output: One

// Safe retrieval
if (numberNames.TryGetValue(2, out string result))
{
    Console.WriteLine($"Key: 2, Value: {result}");
}

// Iteration
foreach (KeyValuePair<int, string> pair in numberNames)
{
    Console.WriteLine($"Key: {pair.Key}, Value: {pair.Value}");
}

Removing items from SortedList

Remove items:

numberNames.Remove(1); // Removes by key
numberNames.RemoveAt(0); // Removes by index
numberNames.Clear(); // Removes all items

SortedList features

Key features:

Console.WriteLine($"Count: {numberNames.Count}");
Console.WriteLine($"Capacity: {numberNames.Capacity}");

if (numberNames.ContainsKey(2))
{
    Console.WriteLine("Key 2 exists");
}

Wrap-up

SortedList offers:

• Automatic sorting
• Fast lookups
• Memory efficiency
• Custom sorting options

Consider SortedList when you need sorted data with quick access, but be mindful of its performance characteristics for large datasets or frequent modifications.

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