There’s no need to call equals if hashCode differs. There’s no need to call hashCode if (obj1 == obj2). There’s no need for hashCode and/or equals just to iterate – you’re not comparing objects When needed to distinguish in between objects.
Use the HashSet<T>.CopyTo method. This method copies the items from the HashSet<T> to an array. So given a HashSet<String> called stringSet you would do something like this: String[] stringArray = new String[stringSet.Count]; stringSet.CopyTo(stringArray);
Nope, you’ve found exactly the solution you’re supposed to use. Even for TreeSet, it’s frowned upon to use comparison criteria that aren’t compatible with equals: Note that the ordering maintained by a sorted set (whether or not an explicit comparator is provided) must be consistent with equals if the sorted set is to correctly implement … Read more
Make sure your object’s class overrides Equals and GetHashCode and then you can pass the List<T> to HashSet<T> constructor. var hashSet = new HashSet<YourType>(yourList); You may see: What is the best algorithm for an overridden System.Object.GetHashCode?
The set will give much better performance (O(n) vs O(n^2) for the list), and that’s normal because set membership (the contains operation) is the very purpose of a set. Contains for a HashSet is O(1) compared to O(n) for a list, therefore you should never use a list if you often need to run contains.
Answer below was written in 2011. It’s now in .NET 4.7.2 and .NET Core 2.0; it will be in .NET Standard 2.1. There’s no technical reason why this shouldn’t be possible – Microsoft just hasn’t chosen to expose a constructor with an initial capacity. If you can call a constructor which takes an IEnumerable<T> and … Read more
Others have already pointed out why it is questionable from a mathematical point of view, by referring to Russell’s paradox. This does not answer your question on a technical level, though. So let’s dissect this: First, once more the relevant part from the JavaDoc of the Set interface: Note: Great care must be exercised if … Read more
It uses equals() to compare the data. Below is from the javadoc for Set adds the specified element e to this set if the set contains no element e2 such that (e==null ? e2==null : e.equals(e2)). The equals() method for String does a character by character comparison. From the javadoc for String The result is … Read more
Just use a set: >>> l = set() >>> l.add(1) >>> l.add(2) >>> 1 in l True >>> 34 in l False The same works for lists: >>> ll = [1,2,3] >>> 2 in ll True >>> 23 in ll False Edit: Note @bholagabbar’s comment below that the time complexity for in checks in lists … Read more
Standard .NET HashSet do not preserve the insertion order. For simple tests the insertion order may be preserved due to an accident, but it’s not guaranteed and would not always work that way. To prove that it is enough to do some removals in between. See this question for more information on that: Does HashSet … Read more