Enumerable.Count 方法

定义

命名空间:

System.Linq

程序集:

System.Linq.dll

返回序列中的元素数量。

重载

Count<TSource>(IEnumerable<TSource>)	返回序列中的元素数量。
Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)	返回表示在指定的序列中满足条件的元素数量的数字。

Count<TSource>(IEnumerable<TSource>)

Source:

Count.cs

返回序列中的元素数量。

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static int Count(System::Collections::Generic::IEnumerable<TSource> ^ source);

public static int Count<TSource> (this System.Collections.Generic.IEnumerable<TSource> source);

static member Count : seq<'Source> -> int

<Extension()>
Public Function Count(Of TSource) (source As IEnumerable(Of TSource)) As Integer

类型参数

TSource

source 的元素类型。

参数

source

IEnumerable<TSource>

包含要计数的元素的序列。

返回

Int32

输入序列中的元素数量。

例外

ArgumentNullException

source 为 null。

OverflowException

中的 source 元素数大于 Int32.MaxValue。

示例

下面的代码示例演示如何使用 Count<TSource>(IEnumerable<TSource>) 对数组中的元素进行计数。

string[] fruits = { "apple", "banana", "mango", "orange", "passionfruit", "grape" };

try
{
    int numberOfFruits = fruits.Count();
    Console.WriteLine(
        "There are {0} fruits in the collection.",
        numberOfFruits);
}
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 6 fruits in the collection.

' Create an array of strings.
Dim fruits() As String = {"apple", "banana", "mango", "orange", "passionfruit", "grape"}

Try
    ' Count the number of items in the array.
    Dim numberOfFruits As Integer = fruits.Count()
    ' Display the output.
    Console.WriteLine($"There are {numberOfFruits} fruits in the collection.")
Catch e As OverflowException
    Console.WriteLine("The count is too large to store as an Int32. Try using LongCount() instead.")
End Try

' This code produces the following output:
'
' There are 6 fruits in the collection.

注解

如果 的类型 source 实现 ICollection<T>，则使用该实现获取元素计数。 否则，此方法确定计数。

LongCount如果预期并且希望允许结果大于 MaxValue，请使用 方法。

在 Visual Basic 查询表达式语法中， Aggregate Into Count() 子句转换为 的 Count调用。

另请参阅

• Aggregate 子句 (Visual Basic)

Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)

Source:

Count.cs

返回表示在指定的序列中满足条件的元素数量的数字。

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static int Count(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, bool> ^ predicate);

public static int Count<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);

static member Count : seq<'Source> * Func<'Source, bool> -> int

<Extension()>
Public Function Count(Of TSource) (source As IEnumerable(Of TSource), predicate As Func(Of TSource, Boolean)) As Integer

类型参数

TSource

source 的元素类型。

参数

source

IEnumerable<TSource>

包含要测试和计数的元素的序列。

predicate

Func<TSource,Boolean>

用于测试每个元素是否满足条件的函数。

返回

Int32

一个数字，表示序列中满足谓词函数条件的元素数量。

例外

ArgumentNullException

source 或 predicate 为 null。

OverflowException

中的 source 元素数大于 Int32.MaxValue。

示例

下面的代码示例演示如何使用 Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 对满足条件的数组中的元素进行计数。

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.

Structure Pet
    Public Name As String
    Public Vaccinated As Boolean
End Structure

Public Shared 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.
        Console.WriteLine($"There are {numberUnvaccinated} unvaccinated animals.")
    Catch e As OverflowException
        Console.WriteLine("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.

注解

如果 的类型 source 实现 ICollection<T>，则使用该实现获取元素计数。 否则，此方法确定计数。

在预期并且希望允许结果大于 MaxValue时，应使用 LongCount 方法。

在 Visual Basic 查询表达式语法中， Aggregate Into Count() 子句转换为 的 Count调用。

另请参阅

• Aggregate 子句 (Visual Basic)