Enumerable.LongCount<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)

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

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


<ExtensionAttribute> _
Public Shared Function LongCount(Of TSource) ( _
    source As IEnumerable(Of TSource), _
    predicate As Func(Of TSource, Boolean) _
) As Long
public static long LongCount<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, bool> predicate

Type Parameters

  • TSource
    The type of the elements of source.


  • predicate
    Type: System.Func<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<TSource>. When you use instance method syntax to call this method, omit the first parameter.


Exception Condition

source or predicate is nulla null reference (Nothing in Visual Basic).


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<TSource>(IEnumerable<TSource>, Func<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.
      outputBlock.Text & ="There are " & count & " animals over age " & Age & vbCrLf
   End Sub

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

      class Pet
         public string Name { get; set; }
         public int Age { get; set; }

      public static void LongCountEx2()
         Pet[] pets = { new Pet { Name="Barley", Age=8 },
                            new Pet { Name="Boots", Age=4 },
                            new Pet { Name="Whiskers", Age=1 } };

         const int Age = 3;

         long count = pets.LongCount(pet => pet.Age > Age);

         outputBlock.Text += String.Format("There are {0} animals over age {1}.", count, Age) + "\n";

       This code produces the following output:

       There are 2 animals over age 3.

Version Information


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0


For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.