What is the JavaScript equivalent to a C# HashSet?
Actually JavaScript provides a Set object, fairly simple to use: var set = new Set(); set.add(1); set.add(2); set.has(1) // true Unfortunately, it is not compatible with IE9.
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HashSet versus Dictionary w.r.t searching time to find if an item exists
HashSet vs List vs Dictionary performance test, taken from here. Add 1000000 objects (without checking duplicates) Contains check for half the objects of a collection of 10000 Remove half the objects of a collection of 10000
Remove Elements from a HashSet while Iterating [duplicate]
You can manually iterate over the elements of the set: Iterator<Integer> iterator = set.iterator(); while (iterator.hasNext()) { Integer element = iterator.next(); if (element % 2 == 0) { iterator.remove(); } } You will often see this pattern using a for loop rather than a while loop: for (Iterator<Integer> i = set.iterator(); i.hasNext();) { Integer element … Read more
Collection that allows only unique items in .NET?
HashSet<T> is what you’re looking for. From MSDN (emphasis added): The HashSet<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. Note that the HashSet<T>.Add(T item) method returns a bool — true if the item was added to the collection; false … Read more
How to sort a HashSet?
A HashSet does not guarantee any order of its elements. If you need this guarantee, consider using a TreeSet to hold your elements. However if you just need your elements sorted for this one occurrence, then just temporarily create a List and sort that: Set<?> yourHashSet = new HashSet<>(); … List<?> sortedList = new ArrayList<>(yourHashSet); … Read more
When should I use the HashSet type?
The important thing about HashSet<T> is right there in the name: it’s a set. The only things you can do with a single set is to establish what its members are, and to check whether an item is a member. Asking if you can retrieve a single element (e.g. set[45]) is misunderstanding the concept of … Read more
How does HashSet compare elements for equality?
It uses an IEqualityComparer<T> (EqualityComparer<T>.Default unless you specify a different one on construction). When you add an element to the set, it will find the hash code using IEqualityComparer<T>.GetHashCode, and store both the hash code and the element (after checking whether the element is already in the set, of course). To look an element up, … Read more
Does adding a duplicate value to a HashSet/HashMap replace the previous value
In the case of HashMap, it replaces the old value with the new one. In the case of HashSet, the item isn’t inserted.
HashSet vs LinkedHashSet
The difference between the two are, as you’ve stated: A LinkedHashSet is an ordered version of HashSet that maintains a doubly-linked List across all elements. Use this class instead of HashSet when you care about the iteration order. When you iterate through a HashSet the order is unpredictable, while a LinkedHashSet lets you iterate through … Read more
Why is HashSet so much slower than HashSet?
There are two perf problems induced by the Point struct. Something you can see when you add Console.WriteLine(GC.CollectionCount(0)); to the test code. You’ll see that the Point test requires ~3720 collections but the string test only needs ~18 collections. Not for free. When you see a value type induce so many collections then you need … Read more