Enumerable.Count Method

Definition

返回序列中的元素数量。Returns the number of elements in a sequence.

Overloads

Count<TSource>(IEnumerable<TSource>)

返回序列中的元素数量。Returns the number of elements in a sequence.

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。Returns a number that represents how many elements in the specified sequence satisfy a condition.

Count<TSource>(IEnumerable<TSource>)

返回序列中的元素数量。Returns the number of elements in a sequence.

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

Type Parameters

TSource

source 的元素类型。The type of the elements of source.

Parameters

source
IEnumerable<TSource>

包含要计数的元素的序列。A sequence that contains elements to be counted.

Returns

Int32

输入序列中的元素数量。The number of elements in the input sequence.

Exceptions

sourcenullsource is null.

source 中的元素数量大于 MaxValueThe number of elements in source is larger than MaxValue.

Examples

下面的代码示例演示如何使用 Count<TSource>(IEnumerable<TSource>) 计算数组中元素的数目。The following code example demonstrates how to use Count<TSource>(IEnumerable<TSource>) to count the elements in an array.

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.

Remarks

如果 source 的类型实现 ICollection<T>,则使用该实现获取元素的计数。If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. 否则,此方法将确定计数。Otherwise, this method determines the count.

当你预期并希望允许结果大于 MaxValue时,请使用 LongCount 方法。Use the LongCount method when you expect and want to allow the result to be greater than MaxValue.

在 Visual Basic 查询表达式语法中,Aggregate Into Count() 子句会转换为 Count调用。In Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count.

See also

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。Returns a number that represents how many elements in the specified sequence satisfy a condition.

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

Type Parameters

TSource

source 的元素类型。The type of the elements of source.

Parameters

source
IEnumerable<TSource>

包含要测试和计数的元素的序列。A sequence that contains elements to be tested and counted.

predicate
Func<TSource,Boolean>

用于测试每个元素是否满足条件的函数。A function to test each element for a condition.

Returns

Int32

一个数字,表示序列中满足谓词函数条件的元素数量。A number that represents how many elements in the sequence satisfy the condition in the predicate function.

Exceptions

sourcepredicatenullsource or predicate is null.

source 中的元素数量大于 MaxValueThe number of elements in source is larger than MaxValue.

Examples

下面的代码示例演示如何使用 Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 来计算数组中满足条件的元素。The following code example demonstrates how to use Count<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 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.

Remarks

如果 source 的类型实现 ICollection<T>,则使用该实现获取元素的计数。If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. 否则,此方法将确定计数。Otherwise, this method determines the count.

如果希望并希望允许结果大于 MaxValue,应使用 LongCount 方法。You should use the LongCount method when you expect and want to allow the result to be greater than MaxValue.

在 Visual Basic 查询表达式语法中,Aggregate Into Count() 子句会转换为 Count调用。In Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count.

See also

Applies to