Enumerable.Take<TSource>(IEnumerable<TSource>, Int32) 方法

定義

從序列開頭傳回指定的連續項目數目。Returns a specified number of contiguous elements from the start of a sequence.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TSource> ^ Take(System::Collections::Generic::IEnumerable<TSource> ^ source, int count);
public static System.Collections.Generic.IEnumerable<TSource> Take<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, int count);
static member Take : seq<'Source> * int -> seq<'Source>
<Extension()>
Public Function Take(Of TSource) (source As IEnumerable(Of TSource), count As Integer) As IEnumerable(Of TSource)

類型參數

TSource

source 項目的類型。The type of the elements of source.

參數

source
IEnumerable<TSource>

傳回項目的序列。The sequence to return elements from.

count
Int32

要傳回的項目數目。The number of elements to return.

傳回

IEnumerable<TSource>

IEnumerable<T>,其中包含輸入序列開頭處指定的項目數目。An IEnumerable<T> that contains the specified number of elements from the start of the input sequence.

例外狀況

sourcenullsource is null.

範例

下列程式碼範例示範如何使用 Take,從序列的開頭傳回元素。The following code example demonstrates how to use Take to return elements from the start of a sequence.

int[] grades = { 59, 82, 70, 56, 92, 98, 85 };

IEnumerable<int> topThreeGrades =
    grades.OrderByDescending(grade => grade).Take(3);

Console.WriteLine("The top three grades are:");
foreach (int grade in topThreeGrades)
{
    Console.WriteLine(grade);
}
/*
 This code produces the following output:

 The top three grades are:
 98
 92
 85
*/
' Create an array of Integer values that represent grades.
Dim grades() As Integer = {59, 82, 70, 56, 92, 98, 85}

' Get the highest three grades by first sorting
' them in descending order and then taking the
' first three values.
Dim topThreeGrades As IEnumerable(Of Integer) =
grades _
.OrderByDescending(Function(grade) grade) _
.Take(3)

' Display the results.
Dim output As New System.Text.StringBuilder("The top three grades are:" & vbCrLf)
For Each grade As Integer In topThreeGrades
    output.AppendLine(grade)
Next
Console.WriteLine(output.ToString())

' This code produces the following output:
'
' The top three grades are:
' 98
' 92
' 85

備註

這個方法是使用延後執行來執行。This method is implemented by using deferred execution. 立即傳回值是一個物件,它會儲存執行動作所需的所有資訊。The immediate return value is an object that stores all the information that is required to perform the action. 在列舉物件之前,不會執行此方法所代表的查詢,方法是直接呼叫其 GetEnumerator 方法,或是在 Visual Basic 中C#使用 Visual 或 For Each 中的 foreachThe query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

Take 列舉 source 並產生元素,直到產生 count 元素,或 source 不包含其他元素為止。Take enumerates source and yields elements until count elements have been yielded or source contains no more elements. 如果 count 超過 source中的元素數目,則會傳回 source 的所有元素。If count exceeds the number of elements in source, all elements of source are returned.

如果 count 小於或等於零,則不會列舉 source,而且會傳回空的 IEnumerable<T>If count is less than or equal to zero, source is not enumerated and an empty IEnumerable<T> is returned.

TakeSkip 方法是可補充的功能。The Take and Skip methods are functional complements. 假設序列 coll 和整數 n,串連 coll.Take(n)coll.Skip(n) 的結果,會產生與 coll相同的順序。Given a sequence coll and an integer n, concatenating the results of coll.Take(n) and coll.Skip(n) yields the same sequence as coll.

在 Visual Basic 查詢運算式語法中,Take 子句會轉譯為 Take的調用。In Visual Basic query expression syntax, a Take clause translates to an invocation of Take.

適用於

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