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.NET Framework Class Library
EnumerableCountTSource Method (IEnumerableTSource, FuncTSource, Boolean)

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

Namespace:   System.Linq
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)
Syntax
<[%$TOPIC/bb535181_en-us_VS_110_1_0_0_0_0%]> _
Public Shared Function Count(Of TSource) ( _
	source As [%$TOPIC/bb535181_en-us_VS_110_1_0_0_0_1%](Of TSource), _
	predicate As [%$TOPIC/bb535181_en-us_VS_110_1_0_0_0_2%](Of TSource, [%$TOPIC/bb535181_en-us_VS_110_1_0_0_0_3%]) _
) As [%$TOPIC/bb535181_en-us_VS_110_1_0_0_0_4%]
public static [%$TOPIC/bb535181_en-us_VS_110_1_0_1_0_0%] Count<TSource>(
	this [%$TOPIC/bb535181_en-us_VS_110_1_0_1_0_1%]<TSource> source,
	[%$TOPIC/bb535181_en-us_VS_110_1_0_1_0_2%]<TSource, [%$TOPIC/bb535181_en-us_VS_110_1_0_1_0_3%]> predicate
)
[[%$TOPIC/bb535181_en-us_VS_110_1_0_2_0_0%]]
public:
generic<typename TSource>
static [%$TOPIC/bb535181_en-us_VS_110_1_0_2_0_1%] Count(
	[%$TOPIC/bb535181_en-us_VS_110_1_0_2_0_2%]<TSource>^ source, 
	[%$TOPIC/bb535181_en-us_VS_110_1_0_2_0_3%]<TSource, [%$TOPIC/bb535181_en-us_VS_110_1_0_2_0_4%]>^ predicate
)
static member Count : 
        source:[%$TOPIC/bb535181_en-us_VS_110_1_0_3_0_0%]<'TSource> * 
        predicate:[%$TOPIC/bb535181_en-us_VS_110_1_0_3_0_1%]<'TSource, [%$TOPIC/bb535181_en-us_VS_110_1_0_3_0_2%]> -> [%$TOPIC/bb535181_en-us_VS_110_1_0_3_0_3%]

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.GenericIEnumerableTSource

A sequence that contains elements to be tested and counted.

predicate
Type: SystemFuncTSource, Boolean

A function to test each element for a condition.

Return Value

Type: SystemInt32
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 IEnumerableTSource. 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).
Exceptions
ExceptionCondition
ArgumentNullException

source or predicate is .

OverflowException

The number of elements in source is larger than MaxValue.

Remarks

If the type of source implements ICollectionT, 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.

Examples

The following code example demonstrates how to use CountTSource(IEnumerableTSource, FuncTSource, 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}}

        Try 
            ' 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.
class Pet
            {
                public string Name { get; set; }
                public bool Vaccinated { get; set; }
            }

            public static void CountEx2()
            {
                Pet[] pets = { new Pet { Name="Barley", Vaccinated=true },
                               new Pet { Name="Boots", Vaccinated=false },
                               new Pet { Name="Whiskers", Vaccinated=false } };

                try
                {
                    int numberUnvaccinated = pets.Count(p => p.Vaccinated == false);
                    Console.WriteLine("There are {0} unvaccinated animals.", numberUnvaccinated);
                }
                catch (OverflowException)
                {
                    Console.WriteLine("The count is too large to store as an Int32.");
                    Console.WriteLine("Try using the LongCount() method instead.");
                }
            }

            // This code produces the following output: 
            // 
            // There are 2 unvaccinated animals.
Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
Platforms

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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