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HashSet<T>.UnionWith Method

.NET Framework 4

Modifies the current HashSet<T> object to contain all elements that are present in itself, the specified collection, or both.

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

Syntax

C++

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public void UnionWith(
	IEnumerable<T> other
)

Parameters

other: Type: System.Collections.Generic.IEnumerable<T>
The collection to compare to the current HashSet<T> object.

Implements

ISet<T>.UnionWith(IEnumerable<T>)

Exceptions

Exception	Condition
ArgumentNullException	other is null.

Remarks

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

Examples

The following example demonstrates how to merge two disparate sets. This example creates two HashSet<T> objects, and populates them with even and odd numbers, respectively. A third HashSet<T> object is created from the set that contains the even numbers. The example then calls the UnionWith method, which adds the odd number set to the third set.

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using System;
using System.Collections.Generic;

class Program
{
    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);
        DisplaySet(evenNumbers);

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

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

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

    }

    private static void DisplaySet(HashSet<int> set)
    {
        Console.Write("{");
        foreach (int i in set)
        {
            Console.Write(" {0}", i);
        }
        Console.WriteLine(" }");
    }
}
/* This example produces output similar to the following:
 * evenNumbers contains 5 elements: { 0 2 4 6 8 }
 * oddNumbers contains 5 elements: { 1 3 5 7 9 }
 * numbers UnionWith oddNumbers...
 * numbers contains 10 elements: { 0 2 4 6 8 1 3 5 7 9 }
 */

Version Information

.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

Reference

HashSet<T> Class

System.Collections.Generic Namespace

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FAQ

AlternateName

Another name for this method would be AddRange. It performs the same basic function as AddRange does on List<T>.

History

4/18/2011
David J. Yaw