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ListDictionary is faster than Hashtable for small collections (10 items or fewer). The Dictionary<TKey,TValue> generic class provides faster lookup than the SortedDictionary<TKey,TValue> generic class.
If you need fast access to elements using index, ArrayList should be choice. If you need fast access to elements using a key, use HashMap. If you need fast add and removal of elements, use LinkedList (but it has a very poor seeking performance).
Advertisements. Collection classes are specialized classes for data storage and retrieval. These classes provide support for stacks, queues, lists, and hash tables. Most collection classes implement the same interfaces.
In the most general case, consider System.Collections.Generic.HashSet as your default "Contains" workhorse data structure, because it takes constant time to evaluate Contains.
The actual answer to "What is the fastest searchable collection" depends on your specific data size, ordered-ness, cost-of-hashing, and search frequency.
If you don't need ordering, try HashSet<Record> (new to .Net 3.5)
If you do, use a List<Record> and call BinarySearch.
Have you considered List.BinarySearch(item)?
You said that your large collection is already sorted so this seems like the perfect opportunity? A hash would definitely be the fastest, but this brings about its own problems and requires a lot more overhead for storage.
You should read this blog that speed tested several different types of collections and methods for each using both single and multi-threaded techniques.
According to the results, a BinarySearch on a List and SortedList were the top performers constantly running neck-in-neck when looking up something as a "value".
When using a collection that allows for "keys", the Dictionary, ConcurrentDictionary, Hashset, and HashTables performed the best overall.
Keep both lists x and y in sorted order.
If x = y, do your action, if x < y, advance x, if y < x, advance y until either list is empty.
The run time of this intersection is proportional to min (size (x), size (y))
Don't run a .Contains () loop, this is proportional to x * y which is much worse.
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