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Enumerable.LongCount(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Boolean))

Returns an Int64 that represents how many elements in a sequence satisfy a condition.

Namespace:  System.Linq
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)

'Declaration
<ExtensionAttribute> _
Public Shared Function LongCount(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	predicate As Func(Of TSource, Boolean) _
) As Long

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)

An IEnumerable(Of T) that contains the elements to be counted.

predicate
Type: System.Func(Of TSource, Boolean)

A function to test each element for a condition.

Return Value

Type: System.Int64
A number that represents how many elements in the sequence satisfy the condition in the predicate function.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(Of TSource). When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
ArgumentNullException

source or predicate is Nothing.

OverflowException

The number of matching elements exceeds MaxValue.

Use this method rather than Count when you expect the result to be greater than MaxValue.

In Visual Basic query expression syntax, an Aggregate Into LongCount() clause translates to an invocation of LongCount.

The following code example demonstrates how to use LongCount(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Boolean)) to count the elements in an array that satisfy a condition.

    Structure Pet
        Public Name As String 
        Public Age As Integer 
    End Structure 

    Sub LongCountEx2()
        ' Create a list of Pet objects. 
        Dim pets As New List(Of Pet)(New Pet() _
                             {New Pet With {.Name = "Barley", .Age = 8}, _
                              New Pet With {.Name = "Boots", .Age = 4}, _
                              New Pet With {.Name = "Whiskers", .Age = 1}})

        ' Determine the number of elements in the list 
        ' where the pet's age is greater than a constant value (3). 
        Const Age As Integer = 3
        Dim count As Long = _
            pets.LongCount(Function(pet) pet.Age > Age)

        ' Display the result.
        MsgBox("There are " & count & " animals over age " & Age)
    End Sub 

    ' This code produces the following output: 
    
    ' There are 2 animals over age 3

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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