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HashSet<T>.TrimExcess Method

Sets the capacity of a HashSet<T> object to the actual number of elements it contains, rounded up to a nearby, implementation-specific value.

Namespace:  System.Collections.Generic
Assembly:  System.Core (in System.Core.dll)
public void TrimExcess()

You can use the TrimExcess method to minimize a HashSet<T> object's memory overhead once it is known that no new elements will be added. To completely clear a HashSet<T> object and release all memory referenced by it, call this method after calling the Clear method.

This method is an O(n) operation, where n is Count.

The following example creates and populates a HashSet<T> collection, and then clears the collection and releases the memory referenced by it.

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

    for (int i = 0; i < 10; i++)

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


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

/* This example produces output similar to the following:
 * Numbers contains 10 elements: { 0 1 2 3 4 5 6 7 8 9 }
 * Numbers contains 0 elements: { }

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

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

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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