HashSet<T>.Contains(T) Method

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

Returns

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

Implements

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.