HashSet<T>.Contains(T) Method

Definition

Namespace:

System.Collections.Generic

Assemblies:

netstandard.dll, System.Collections.dll

Source:

HashSet.cs

Determines whether a HashSet<T> object contains the specified element.

public:
 virtual bool Contains(T item);

public bool Contains(T item);

abstract member Contains : 'T -> bool
override this.Contains : 'T -> bool

Public Function Contains (item As T) As Boolean

Parameters

item

T

The element to locate in the HashSet<T> object.

Returns

Boolean

true if the HashSet<T> object contains the specified element; otherwise, false.

Implements

Contains(T) Contains(T)

Examples

The following example demonstrates how to remove values from a HashSet<T> collection using the Remove method. In this example, the Contains method verifies that the set contains a value before removing it.

HashSet<int> numbers = new HashSet<int>();

for (int i = 0; i < 20; i++) {
    numbers.Add(i);
}

// Display all the numbers in the hash table.
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

// Remove all odd numbers.
numbers.RemoveWhere(IsOdd);
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

// Check if the hash table contains 0 and, if so, remove it.
if (numbers.Contains(0)) {
    numbers.Remove(0);
}
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);

bool IsOdd(int i)
{
    return ((i % 2) == 1);
}

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

    Console.WriteLine(" }");
}

// This example displays the following output:
//    numbers contains 20 elements: { 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 }
//    numbers contains 10 elements: { 0 2 4 6 8 10 12 14 16 18 }
//    numbers contains 9 elements: { 2 4 6 8 10 12 14 16 18 }

let isOdd i = i % 2 = 1

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

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

    printfn " }"

let numbers = HashSet<int>()

for i in 1..20 do
    numbers.Add i |> ignore

// Display all the numbers in the hash table.
printf $"numbers contains {numbers.Count} elements: "
displaySet numbers

// Remove all odd numbers.
numbers.RemoveWhere isOdd |> ignore
printf $"numbers contains {numbers.Count} elements: "
displaySet numbers

// Check if the hash table contains 0 and, if so, remove it.
if numbers.Contains 0 then
    numbers.Remove 0 |> ignore

printf $"numbers contains {numbers.Count} elements: "
displaySet numbers
// This example displays the following output:
//    numbers contains 20 elements: { 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 }
//    numbers contains 10 elements: { 0 2 4 6 8 10 12 14 16 18 }
//    numbers contains 9 elements: { 2 4 6 8 10 12 14 16 18 }

Imports System.Collections.Generic

Module Example
    Public Sub Main()
        Dim numbers As New HashSet(Of Integer)()

        For i As Integer = 0 To 19
            numbers.Add(i)
        Next i

        ' Display all the numbers in the hash table.
        Console.Write("numbers contains {0} elements: ", numbers.Count)
        DisplaySet(numbers)

        ' Remove all odd numbers.
        numbers.RemoveWhere(AddressOf IsOdd)
        Console.Write("numbers contains {0} elements: ", numbers.Count)
        DisplaySet(numbers)

        ' Check if the hash table contains 0 and, if so, remove it.
        If numbers.Contains(0) Then
            numbers.Remove(0)
        End If
        Console.Write("numbers contains {0} elements: ", numbers.Count)
        DisplaySet(numbers)
    End Sub

    Private Function IsOdd(ByVal i As Integer) As Boolean
        Return ((i Mod 2) = 1)
    End Function

    Private Sub DisplaySet(ByVal coll As HashSet(Of Integer))
        Console.Write("{")
        For Each i As Integer In coll
            Console.Write(" {0}", i)
        Next
        Console.WriteLine(" }")
    End Sub
End Module
' The example displays the following output:
'    numbers contains 20 elements: { 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 }
'    numbers contains 10 elements: { 0 2 4 6 8 10 12 14 16 18 }
'    numbers contains 9 elements: { 2 4 6 8 10 12 14 16 18 }

Remarks

This method is an O(1) operation.