OrderedDictionary<TKey, TValue>

The OrderedDictionary<TKey, TValue> is a generic collection that maintains the insertion order of its elements. It implements the IDictionary<TKey, TValue>, IReadOnlyDictionary<TKey, TValue>, and IList<KeyValuePair<TKey, TValue>> interfaces, providing both key-based lookup and index-based access. This makes it especially useful in environments like Unity with Mono, where the standard OrderedDictionary is not available.

Features

• Maintains Insertion Order: Elements are stored in the order they are added.
• Dual Access: Retrieve items by key or by index.
• Interfaces Implemented: Supports standard dictionary and list interfaces.
• Unity Compatibility: Serves as an alternative in environments (like Unity with Mono) that lack a built-in ordered dictionary.

Complexity (Big-O Notation)

• Add: O(1).
• Remove: O(n) worst-case due to re-indexing of the underlying list.
• Lookup by key: O(1).
• Lookup by index: O(1).
• Insert (by index): O(n) worst-case.
• Clear: O(n)

Usage Example

using Collections.OrderedDictionary;

var dict = new OrderedDictionary<string, int>();

// Add items
dict.Add("apple", 1);
dict["banana"] = 2;

// Access items by key
int appleValue = dict["apple"];
Console.WriteLine(appleValue); // Output: 1

// Update value by key
dict["banana"] = 3;
Console.WriteLine(dict["banana"]); // Output: 3

Conclusion

The OrderedDictionary<TKey, TValue> offers a robust solution for maintaining insertion order while allowing fast key-based lookups and index-based access. This makes it an ideal choice for projects, particularly in environments like Unity with Mono, where a built-in ordered dictionary is unavailable.