What is SortedDictionary in C#: Explanation and Example

SortedDictionary in C# is a collection that stores key-value pairs in sorted order by keys. It automatically keeps the keys sorted, unlike a regular dictionary which has no order. This makes it useful when you need fast lookups and ordered data.

How It Works

Think of SortedDictionary like a well-organized filing cabinet where each file (key) is placed in alphabetical order. When you add a new file, it automatically finds the right spot so everything stays sorted. This means you can quickly find any file without searching through a messy pile.

Under the hood, SortedDictionary uses a balanced tree structure to keep keys sorted. This allows it to add, remove, or find items efficiently while maintaining order. Unlike a regular dictionary that stores items randomly, SortedDictionary always keeps the keys in order, which is helpful when you want to process data in a sorted way.

Example

This example shows how to create a SortedDictionary, add some items, and print them in sorted order by key.

csharp

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        SortedDictionary<int, string> sortedDict = new SortedDictionary<int, string>();

        sortedDict.Add(3, "Apple");
        sortedDict.Add(1, "Banana");
        sortedDict.Add(2, "Cherry");

        foreach (var item in sortedDict)
        {
            Console.WriteLine($"Key: {item.Key}, Value: {item.Value}");
        }
    }
}

Output

Key: 1, Value: Banana
Key: 2, Value: Cherry
Key: 3, Value: Apple

When to Use

Use SortedDictionary when you need to keep data sorted by keys automatically and want fast lookups, insertions, and deletions. It is great for scenarios like:

• Maintaining a leaderboard where scores (keys) must stay sorted.
• Storing configuration settings that need to be processed in order.
• Implementing caches or indexes where order matters.

If you don't need sorted keys, a regular Dictionary might be faster. But when order is important, SortedDictionary is a simple and efficient choice.

Key Points

• Sorted by keys: Automatically keeps keys in sorted order.
• Balanced tree: Uses a tree structure for efficient operations.
• Fast lookups: Provides quick access to values by key.
• Use case: Best when order of keys matters.
• Not thread-safe: Requires external synchronization in multithreaded scenarios.

Key Takeaways

SortedDictionary stores key-value pairs sorted by keys automatically.

It uses a balanced tree for efficient add, remove, and lookup operations.

Use it when you need ordered data with fast access by key.

Regular Dictionary is faster if order does not matter.

SortedDictionary is not thread-safe without extra handling.