IsSubsetOf Method

HashSet<T>.IsSubsetOf Method (IEnumerable<T>)

 

Determines whether a HashSet<T> object is a subset of the specified collection.

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

public bool IsSubsetOf(
	IEnumerable<T> other
)

Parameters

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

The collection to compare to the current HashSet<T> object.

Return Value

Type: System.Boolean

true if the HashSet<T> object is a subset of other; otherwise, false.

Exception Condition
ArgumentNullException

other is null.

An empty set is a subset of any other collection, including an empty set; therefore, this method returns true if the collection represented by the current HashSet<T> object is empty, even if the other parameter is an empty set.

This method always returns false if Count is greater than the number of elements in other.

If the collection represented by other is a HashSet<T> collection with the same equality comparer as the current HashSet<T> object, this method is an O(n) operation. Otherwise, this method is an O(n + m) operation, where n is Count and m is the number of elements in other.

The following example creates two disparate HashSet<T> objects and compares them to each other. In this example, lowNumbers is both a subset and a proper subset of allNumbers until allNumbers is modified, using the IntersectWith method, to contain only values that are present in both sets. Once allNumbers and lowNumbers are identical, lowNumbers is still a subset of allNumbers but is no longer a proper subset.

static void Main()
{
    HashSet<int> lowNumbers = new HashSet<int>();
    HashSet<int> allNumbers = new HashSet<int>();

    for (int i = 1; i < 5; i++)
    {
        lowNumbers.Add(i);
    }

    for (int i = 0; i < 10; i++)
    {
        allNumbers.Add(i);
    }

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

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

    Console.WriteLine("lowNumbers overlaps allNumbers: {0}",
        lowNumbers.Overlaps(allNumbers));

    Console.WriteLine("allNumbers and lowNumbers are equal sets: {0}",
        allNumbers.SetEquals(lowNumbers));

    // Show the results of sub/superset testing
    Console.WriteLine("lowNumbers is a subset of allNumbers: {0}",
        lowNumbers.IsSubsetOf(allNumbers));
    Console.WriteLine("allNumbers is a superset of lowNumbers: {0}",
        allNumbers.IsSupersetOf(lowNumbers));
    Console.WriteLine("lowNumbers is a proper subset of allNumbers: {0}",
        lowNumbers.IsProperSubsetOf(allNumbers));
    Console.WriteLine("allNumbers is a proper superset of lowNumbers: {0}",
        allNumbers.IsProperSupersetOf(lowNumbers));

    // Modify allNumbers to remove numbers that are not in lowNumbers.
    allNumbers.IntersectWith(lowNumbers);
    Console.Write("allNumbers contains {0} elements: ", allNumbers.Count);
    DisplaySet(allNumbers);

    Console.WriteLine("allNumbers and lowNumbers are equal sets: {0}",
        allNumbers.SetEquals(lowNumbers));

    // Show the results of sub/superset testing with the modified set.
    Console.WriteLine("lowNumbers is a subset of allNumbers: {0}",
        lowNumbers.IsSubsetOf(allNumbers));
    Console.WriteLine("allNumbers is a superset of lowNumbers: {0}",
        allNumbers.IsSupersetOf(lowNumbers));
    Console.WriteLine("lowNumbers is a proper subset of allNumbers: {0}",
        lowNumbers.IsProperSubsetOf(allNumbers));
    Console.WriteLine("allNumbers is a proper superset of lowNumbers: {0}",
        allNumbers.IsProperSupersetOf(lowNumbers));
}
/* This code example produces output similar to the following:
 * lowNumbers contains 4 elements: { 1 2 3 4 }
 * allNumbers contains 10 elements: { 0 1 2 3 4 5 6 7 8 9 }
 * lowNumbers overlaps allNumbers: True
 * allNumbers and lowNumbers are equal sets: False
 * lowNumbers is a subset of allNumbers: True
 * allNumbers is a superset of lowNumbers: True
 * lowNumbers is a proper subset of allNumbers: True
 * allNumbers is a proper superset of lowNumbers: True
 * allNumbers contains 4 elements: { 1 2 3 4 }
 * allNumbers and lowNumbers are equal sets: True
 * lowNumbers is a subset of allNumbers: True
 * allNumbers is a superset of lowNumbers: True
 * lowNumbers is a proper subset of allNumbers: False
 * allNumbers is a proper superset of lowNumbers: False
 */

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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