hashset

I am looking if there is a pre-existing .Net 'Hash-Set type' implementation suitable to atomizing a general type T. We have a large number of identical objects coming in for serialized sources that need to be atomized to conserve memory. A Dictionary<T,T> with the value == key works perfectly, however the objects in these collections can run into the millions across the app, and so it seem very wasteful to store 2 references to every object. HashSet cannot be used as it only has Contains, there ?is no way? to get to the actual member instance. Obviously I could roll my own but wanted to check

I'm creating my own HashSet that works as the standard HashSet, using a Dictionary. I'm doing this because C# for XNA XBox doesn't support HashSets. This code is based on code from an example I found. I've edited the example to fix some of the problems but it still won't compile. public class HashSet2<T> : ICollection<T> { private Dictionary<T, Int16> dict; // code has been edited out of this example // see further on in the question for the full class public IEnumerator<T> GetEnumerator() { throw new NotImplementedException(); } IEnumerator<T> IEnumerable<T>.GetEnumerator() { return dict

I learned that HashSet implements the IEnumerable interface. Thus, it is possible to implicitly cast a HashSet object into IEnumerable : HashSet<T> foo = new HashSet<T>(); IEnumerable<T> foo2 = foo; // Implicit cast, everything fine. This works for nested generic types, too: HashSet<HashSet<T>> dong = new HashSet<HashSet<T>>(); IEnumerable<IEnumerable<T>> dong2 = dong; // Implicit cast, everything fine. At least that's what I thought. But if I make a Dictionary , I run into a problem: IDictionary<T, HashSet<T>> bar = new Dictionary<T, HashSet<T>>(); IDictionary<T, IEnumerable<T>> bar2 = bar; /

I have array of Strings which actually in nothing but list of integers coming from file. I converted it to HashSet so as to remove duplicates as follows: Set<String> intSet = new HashSet<String>(Arrays.asList(strArr)); I expected that it all the numbers to be in order but off course, since this is a string and not integer list, it may not come in order. But whenever I try to print this HashSet, I always get output as follows: [3, 2, 1, 4] [3, 2, 5, 4] Every time, if 3 is present it is considered to be first element. I am not getting why it is acting this way? Can anyone please explain me this.

I have a struct that has, among other data, a unique id : struct Foo { id: u32, other_data: u32, } I want to use the id as the key and keep it inside of the struct: use std::collections::HashSet; use std::hash::{Hash, Hasher}; impl PartialEq for Foo { fn eq(&self, other: &Foo) -> bool { self.id == other.id } } impl Eq for Foo {} impl Hash for Foo { fn hash<H: Hasher>(&self, state: &mut H) { self.id.hash(state); } } This works: pub fn bar() { let mut baz: HashSet<Foo> = HashSet::new(); baz.insert(Foo { id: 1, other_data: 2, }); let other_data = baz.get(&Foo { id: 1, other_data: 0, }).unwrap()

I do not understand why hastable's rehash complexity may be quadratic in worst case at : http://www.cplusplus.com/reference/unordered_set/unordered_multiset/reserve/ Any help would be appreciated ! Thanks Just some basics: Hash collisions is when two or more elements take on the same hash. This can cause worst-case O(n) operations. I won't really go into this much further, since one can find many explanations of this. Basically all the elements can have the same hash, thus you'll have one big linked-list at that hash containing all your elements (and search on a linked-list is of course O(n) )