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

Returns a number that represents how many elements in the specified sequence satisfy a condition.

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

<ExtensionAttribute> _
Public Shared Function Count(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	predicate As Func(Of TSource, Boolean) _
) As Integer

Type Parameters


The type of the elements of source.


Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence that contains elements to be tested and counted.
Type: System.Func(Of TSource, Boolean)
A function to test each element for a condition.

Return Value

Type: System.Int32
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).


source or predicate is Nothing.


The number of elements in source is larger than MaxValue.

If the type of source implements ICollection(Of T), that implementation is used to obtain the count of elements. Otherwise, this method determines the count.

You should use the LongCount method when you expect and want to allow the result to be greater than MaxValue.

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

The following code example demonstrates how to use Count(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 Vaccinated As Boolean
    End Structure

    Sub CountEx2()
        ' Create an array of Pet objects.
        Dim pets() As Pet = {New Pet With {.Name = "Barley", .Vaccinated = True}, _
                             New Pet With {.Name = "Boots", .Vaccinated = False}, _
                             New Pet With {.Name = "Whiskers", .Vaccinated = False}}

            ' Count the number of Pets in the array where the Vaccinated property is False.
            Dim numberUnvaccinated As Integer = _
                pets.Count(Function(p) p.Vaccinated = False)
            ' Display the output.
            MsgBox("There are " & numberUnvaccinated & " unvaccinated animals.")
        Catch e As OverflowException
            MsgBox("The count is too large to store as an Int32. Try using LongCount() instead.")
        End Try

    End Sub

    ' This code produces the following output:
    ' There are 2 unvaccinated animals.

.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.