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HashSet<T> Constructor (IEnumerable<T>)

Initializes a new instance of the HashSet<T> class that uses the default equality comparer for the set type, contains elements copied from the specified collection, and has sufficient capacity to accommodate the number of elements copied.

Namespace:  System.Collections.Generic
Assemblies:   System.Core (in System.Core.dll)
  System.Collections (in System.Collections.dll)

public HashSet(
	IEnumerable<T> collection


Type: System.Collections.Generic.IEnumerable<T>

The collection whose elements are copied to the new set.


collection is null.

The capacity of a HashSet<T> object is the number of elements that the object can hold. A HashSet<T> object's capacity automatically increases as elements are added to the object.

If collection contains duplicates, the set will contain one of each unique element. No exception will be thrown. Therefore, the size of the resulting set is not identical to the size of collection.

This constructor is an O(n) operation, where n is the number of elements in the collection parameter.

The following example shows how to create a HashSet<T> collection from an existing set. In this example, two sets are created with even and odd integers, respectively. A third HashSet<T> object is then created from the even integer set.

static void Main()
    HashSet<int> evenNumbers = new HashSet<int>();
    HashSet<int> oddNumbers = new HashSet<int>();

    for (int i = 0; i < 5; i++)
        // Populate numbers with just even numbers.
        evenNumbers.Add(i * 2);

        // Populate oddNumbers with just odd numbers.
        oddNumbers.Add((i * 2) + 1);

    Console.Write("evenNumbers contains {0} elements: ", evenNumbers.Count);

    Console.Write("oddNumbers contains {0} elements: ", oddNumbers.Count);

    // Create a new HashSet populated with even numbers.
    HashSet<int> numbers = new HashSet<int>(evenNumbers);
    Console.WriteLine("numbers UnionWith oddNumbers...");

    Console.Write("numbers contains {0} elements: ", numbers.Count);


.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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