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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
)

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.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source or predicate is null.

OverflowException

The number of matching elements exceeds MaxValue.

Use this method rather than Count<TSource> 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<TSource>.

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.
*/

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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