Enumerable.Count メソッド

定義

シーケンス内の要素数を返します。Returns the number of elements in a sequence.

オーバーロード

Count<TSource>(IEnumerable<TSource>)

シーケンス内の要素数を返します。Returns the number of elements in a sequence.

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

条件を満たす、指定されたシーケンス内の要素の数を表す数値を返します。Returns a number that represents how many elements in the specified sequence satisfy a condition.

Count<TSource>(IEnumerable<TSource>)

シーケンス内の要素数を返します。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

型パラメーター

TSource

source の要素の型。The type of the elements of source.

パラメーター

source
IEnumerable<TSource>

カウントする要素が格納されているシーケンス。A sequence that contains elements to be counted.

戻り値

Int32

入力シーケンス内の要素数。The number of elements in the input sequence.

例外

sourcenullです。source is null.

source 内の要素数が MaxValue を超えています。The number of elements in source is larger than MaxValue.

次のコード例は、を使用し Count<TSource>(IEnumerable<TSource>) て配列内の要素をカウントする方法を示しています。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.

注釈

の型がを実装している場合 source ICollection<T> は、その実装を使用して要素の数を取得します。If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. それ以外の場合、このメソッドはカウントを決定します。Otherwise, this method determines the count.

を使用する場合は、メソッドを使用し LongCount ます。これにより、結果をよりも大きくすることができ MaxValue ます。Use the LongCount method when you expect and want to allow the result to be greater than MaxValue.

Visual Basic のクエリ式の構文では、 Aggregate Into Count() 句はの呼び出しに変換 Count します。In Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count.

こちらもご覧ください

適用対象

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

条件を満たす、指定されたシーケンス内の要素の数を表す数値を返します。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

型パラメーター

TSource

source の要素の型。The type of the elements of source.

パラメーター

source
IEnumerable<TSource>

テストおよびカウントする要素が格納されているシーケンス。A sequence that contains elements to be tested and counted.

predicate
Func<TSource,Boolean>

各要素が条件を満たしているかどうかをテストする関数。A function to test each element for a condition.

戻り値

Int32

述語関数の条件を満たす、シーケンス内の要素数を表す数値。A number that represents how many elements in the sequence satisfy the condition in the predicate function.

例外

source または predicatenull です。source or predicate is null.

source 内の要素数が MaxValue を超えています。The number of elements in source is larger than MaxValue.

次のコード例は、を使用して、 Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) 条件を満たす配列内の要素をカウントする方法を示しています。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.

注釈

の型がを実装している場合 source ICollection<T> は、その実装を使用して要素の数を取得します。If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. それ以外の場合、このメソッドはカウントを決定します。Otherwise, this method determines the count.

を使用する場合は、メソッドを使用し LongCount て、結果をよりも大きくすることを許可する必要があり MaxValue ます。You should use the LongCount method when you expect and want to allow the result to be greater than MaxValue.

Visual Basic のクエリ式の構文では、 Aggregate Into Count() 句はの呼び出しに変換 Count します。In Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count.

こちらもご覧ください

適用対象