Question

Is there any real practical difference between a SortedList<TKey,TValue> and a SortedDictionary<TKey,TValue>? 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 SortedDictionary<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
SortedList<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>.

(SortedList actually maintains a sorted array, rather than using a tree. It still uses binary search to find elements.)