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

定义

从序列的开头返回指定数量的相邻元素。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)

类型参数

TSource

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

参数

source
IEnumerable<TSource>

要从其返回元素的序列。The sequence to return elements from.

count
Int32

要返回的元素数量。The number of elements to return.

返回

IEnumerable<TSource>

一个 IEnumerable<T>,包含输入序列开头的指定数量的元素。An IEnumerable<T> that contains the specified number of elements from the start of the input sequence.

例外

sourcenullsource is null.

示例

下面的代码示例演示如何使用 Take 从序列的开头返回元素。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

注解

此方法是使用延迟执行实现的。This method is implemented by using deferred execution. 即时返回值是一个对象,该对象存储执行操作所需的所有信息。The immediate return value is an object that stores all the information that is required to perform the action. 此方法表示的查询在枚举对象之前不会执行,方法是通过直接调用 GetEnumerator 方法或在 Visual Basic 中使用视觉C#对象中的 foreachFor Each 来枚举对象。The 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 枚举 source 并生成元素,直到生成 count 元素,或 source 不包含其他元素。Take enumerates source and yields elements until count elements have been yielded or source contains no more elements. 如果 count 超出了 source中的元素数,则返回 source 的所有元素。If count exceeds the number of elements in source, all elements of source are returned.

如果 count 小于或等于零,则不会枚举 source 并且返回空的 IEnumerable<T>If count is less than or equal to zero, source is not enumerated and an empty IEnumerable<T> is returned.

TakeSkip 方法是功能补充。The Take and Skip methods are functional complements. 给定一个序列 coll 和一个整数 n,将 coll.Take(n)coll.Skip(n) 的结果连接起来与 coll生成相同的序列。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 查询表达式语法中,Take 子句会转换为 Take调用。In Visual Basic query expression syntax, a Take clause translates to an invocation of Take.

适用于

另请参阅