Does anyone know if there is a good equivalent to Java's Set collection in C#? I know that you can somewhat mimic a set using a Dictionary or a HashTable by populating but ignoring the values, but that's not a very elegant way.
7 Answers
If you're using .NET 3.5, you can use HashSet<T>. It's true that .NET doesn't cater for sets as well as Java does though.
The Wintellect PowerCollections may help too.
Try HashSet:
The HashSet(Of T) class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order...
The capacity of a HashSet(Of T) object is the number of elements that the object can hold. A HashSet(Of T) object's capacity automatically increases as elements are added to the object.
The HashSet(Of T) class is based on the model of mathematical sets and provides high-performance set operations similar to accessing the keys of the Dictionary(Of TKey, TValue) or Hashtable collections. In simple terms, the HashSet(Of T) class can be thought of as a Dictionary(Of TKey, TValue) collection without values.
A HashSet(Of T) collection is not sorted and cannot contain duplicate elements...
If you're using .NET 4.0 or later:
In the case where you need sorting then use SortedSet<T>. Otherwise if you don't, then use HashSet<T> since it's O(1) for search and manipulate operations. Whereas SortedSet<T> is O(log n) for search and manipulate operations.
I use Iesi.Collections
It's used in lot of OSS projects, I first came across it in NHibernate
I use a wrapper around a Dictionary<T, object>, storing nulls in the values. This gives O(1) add, lookup and remove on the keys, and to all intents and purposes acts like a set.
Have a look at PowerCollections over at CodePlex. Apart from Set and OrderedSet it has a few other usefull collection types such as Deque, MultiDictionary, Bag, OrderedBag, OrderedDictionary and OrderedMultiDictionary.
For more collections, there is also the C5 Generic Collection Library.
I know this is an old thread, but I was running into the same problem and found HashSet to be very unreliable because given the same seed, GetHashCode() returned different codes. So, I thought, why not just use a List and hide the add method like this
public class UniqueList<T> : List<T>
{
public new void Add(T obj)
{
if(!Contains(obj))
{
base.Add(obj);
}
}
}
Because List uses the Equals method solely to determine equality, you can define the Equals method on your T type to make sure you get the desired results.
