What's the difference between SortedList and SortedDictionary?

Question

Maybe a silly question, but is there any real practical difference between a SortedList and a SortedDictionary? Are there any circumstances where you would specifically use one and not the other?

Answer 1

Yes - their performance characteristics differ significantly. It would probably be better to call them SortedList and SortedTree as that reflects the implementation more closely.

Look at the MSDN docs for each of them (SortedList, SortedDictionary) for details of the performance for different operations in different situtations. Here's a nice summary (from the SortedDictionary docs):

The SortedList<TKey, TValue> generic class is a binary search tree with O(log n) retrieval, where n is the number of elements in the dictionary. In this, it is similar to the SortedDictionary<TKey, TValue> generic class. The two classes have similar object models, and both have O(log n) retrieval. Where the two classes differ is in memory use and speed of insertion and removal:

• SortedList<TKey, TValue> uses less memory than SortedDictionary<TKey, TValue>.

• SortedDictionary<TKey, TValue> has faster insertion and removal operations for unsorted data, O(log n) as opposed to O(n) for SortedList<TKey, TValue>.

• If the list is populated all at once from sorted data, SortedList<TKey, TValue> is faster than SortedDictionary<TKey, TValue>.

Answer 2

Check out the MSDN page for SortedList:

From Remarks section:

The SortedList<(Of <(TKey, TValue>)>) generic class is a binary search tree with O(log n) retrieval, where n is the number of elements in the dictionary. In this, it is similar to the SortedDictionary<(Of <(TKey, TValue>)>) generic class. The two classes have similar object models, and both have O(log n) retrieval. Where the two classes differ is in memory use and speed of insertion and removal:

• SortedList<(Of <(TKey, TValue>)>) uses less memory than SortedDictionary<(Of <(TKey, TValue>)>).

• SortedDictionary<(Of <(TKey, TValue>)>) has faster insertion and removal operations for unsorted data, O(log n) as opposed to O(n) for SortedList<(Of <(TKey, TValue>)>).

• If the list is populated all at once from sorted data, SortedList<(Of <(TKey, TValue>)>) is faster than SortedDictionary<(Of <(TKey, TValue>)>).