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

Definition

Namespace:

System.Collections.Generic

Assembly:

System.Collections.dll

Source:

HashSet.cs

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

public:
 virtual bool IsSubsetOf(System::Collections::Generic::IEnumerable<T> ^ other);

public bool IsSubsetOf (System.Collections.Generic.IEnumerable<T> other);

abstract member IsSubsetOf : seq<'T> -> bool
override this.IsSubsetOf : seq<'T> -> bool

Public Function IsSubsetOf (other As IEnumerable(Of T)) As Boolean

Parameters

other

IEnumerable<T>

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

Returns

Boolean

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

Implements

IsSubsetOf(IEnumerable<T>) IsSubsetOf(IEnumerable<T>)

Exceptions

ArgumentNullException

other is null.

Examples

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.

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));

void DisplaySet(HashSet<int> set)
{
    Console.Write("{");
    foreach (int i in set)
    {
        Console.Write(" {0}", i);
    }
    Console.WriteLine(" }");
}

/* 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
*/

let displaySet (set: HashSet<int>) =
    printf "{"

    for i in set do
        printf $" {i}"

    printfn " }"

let lowNumbers = HashSet<int>()
let allNumbers = HashSet<int>()

for i = 1 to 4 do
    lowNumbers.Add i |> ignore


for i = 0 to 9 do
    allNumbers.Add i |> ignore

printf $"lowNumbers contains {lowNumbers.Count} elements: "
displaySet lowNumbers

printf $"allNumbers contains {allNumbers.Count} elements: "
displaySet allNumbers

printfn $"lowNumbers overlaps allNumbers: {lowNumbers.Overlaps allNumbers}"

printfn $"allNumbers and lowNumbers are equal sets: {allNumbers.SetEquals lowNumbers}"

// Show the results of sub/superset testing
printfn $"lowNumbers is a subset of allNumbers: {lowNumbers.IsSubsetOf allNumbers}"
printfn $"allNumbers is a superset of lowNumbers: {allNumbers.IsSupersetOf lowNumbers}"
printfn $"lowNumbers is a proper subset of allNumbers: {lowNumbers.IsProperSubsetOf allNumbers}"
printfn $"allNumbers is a proper superset of lowNumbers: {allNumbers.IsProperSupersetOf lowNumbers}"

// Modify allNumbers to remove numbers that are not in lowNumbers.
allNumbers.IntersectWith lowNumbers
printf $"allNumbers contains {allNumbers.Count} elements: "
displaySet allNumbers

printfn $"allNumbers and lowNumbers are equal sets: {allNumbers.SetEquals lowNumbers}"

// Show the results of sub/superset testing with the modified set.
printfn $"lowNumbers is a subset of allNumbers: {lowNumbers.IsSubsetOf allNumbers}"
printfn $"allNumbers is a superset of lowNumbers: {allNumbers.IsSupersetOf lowNumbers}"
printfn $"lowNumbers is a proper subset of allNumbers: {lowNumbers.IsProperSubsetOf allNumbers}"
printfn $"allNumbers is a proper superset of lowNumbers: {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

Shared Sub Main()

    Dim lowNumbers As HashSet(Of Integer) = New HashSet(Of Integer)()
    Dim allNumbers As HashSet(Of Integer) = New HashSet(Of Integer)()

    For i As Integer = 1 To 4
        lowNumbers.Add(i)
    Next i

    For i As Integer = 0 To 9
        allNumbers.Add(i)
    Next 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))
End Sub
' 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

Remarks

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.