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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.

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);

         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.
      */



Silverlight

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.

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