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

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

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

public static long LongCount<TSource>(
	this IEnumerable<TSource> source,
	Func<TSource, bool> predicate
)

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>

An IEnumerable<T> that contains the elements to be counted.

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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
ArgumentNullException

source or predicate is null.

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<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) to count the elements in an array that satisfy a condition.

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);

    Console.WriteLine("There are {0} animals over age {1}.", count, Age);
}

/*
 This code produces the following output:

 There are 2 animals over age 3.
*/

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0

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