hashset

When working with HashSets in C#, I recently came across an annoying problem: HashSets don't guarantee unicity of the elements; they are not Sets. What they do guarantee is that when Add(T item) is called the item is not added if for any item in the set item.equals(that) is true . This holds no longer if you manipulate items already in the set. A small program that demonstrates (copypasta from my Linqpad): void Main() { HashSet<Tester> testset = new HashSet<Tester>(); testset.Add(new Tester(1)); testset.Add(new Tester(2)); foreach(Tester tester in testset){ tester.Dump(); } foreach(Tester

I found that there is an implementation of a Set that uses hashes (with all the useful consequences, like O(1) for contains() etc) that is claimed to be more efficient than java.util.HashSet in every aspect: http://ontopia.wordpress.com/2009/09/23/a-faster-and-more-compact-set/ http://alias-i.com/lingpipe/docs/api/com/aliasi/util/CompactHashSet.html Would it then be a good idea to quit using java.util.HashSet completely wherever I need a java.util.Set in favor of com.aliasi.util.CompactHashSet ? Let's start a little benchmark game. Benchmarks are based on benchmarks from the original article,

Like the title says, i would like to get a thread-safe HashSet using Guava Collections. Can you help me? Thanks! Set<K> set = Collections.newSetFromMap(new ConcurrentHashMap<K, Boolean>()); This would be the right answer, Using the Sets class from Guava. Anyway the answer from @crhis was good intended. Sets.newSetFromMap(new ConcurrentHashMap<V, Boolean>()); Etienne Neveu Google Collections had a factory method named Sets.newConcurrentHashSet() for a while. Its implementation was similar to Chris's suggestion: public static <E> Set<E> newConcurrentHashSet() { return newSetFromMap(new

Check out this piece of code from Linq.Enumerable class: static IEnumerable<TSource> DistinctIterator<TSource>(IEnumerable<TSource> source, IEqualityComparer<TSource> comparer) { Set<TSource> set = new Set<TSource>(comparer); foreach (TSource element in source) if (set.Add(element)) yield return element; } Why did the guys at Microsoft decided to use this internal implementation of Set and not the regular HashSet ? If it's better in any way, why not exposing it to the public? The implementation of this Set<T> is far simpler than HashSet<T> as it is only needs to add and remove elements and

I'm very confused by Scala's HashSet and Set types as they both seem to do the same thing. What is the difference between them? Is it the same in Java? In my reference it says that HashSet is an "explicit set class" (as compared to Set ). What does that mean? Ben James Scala's mutable and immutable HashSet implementations are concrete classes which you can instantiate. For example, if you explicitly ask for a new scala.collection.immutable.HashSet , you will always get a set which is implemented by a hash trie. There are other set implementations, such as ListSet , which uses a list. Set is a

I have 2 class'es that are handled by NHibernate : AssetGroup , Asset The AssetGroup has a ISet _assets collection. The constructor of AssetGroup will say _assets = new HashSet<Asset>(); I have some operation to add , remove asset in AssetGroup public abstract class Entity<Tid> { public virtual Tid Id { get; protected set; } public override bool Equals(object obj) { return Equals(obj as Entity<Tid>); } public static bool IsTransient(Entity<Tid> obj) { return obj != null && Equals(obj.Id, default(Tid)); } private Type GetUnproxiedType() { return GetType(); } public virtual bool Equals(Entity