Enumerable.Where Enumerable.Where Enumerable.Where Enumerable.Where Method

定義

根據述詞來篩選值序列。Filters a sequence of values based on a predicate.

多載

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

根據述詞來篩選值序列。Filters a sequence of values based on a predicate.

Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>)

根據述詞來篩選值序列。Filters a sequence of values based on a predicate. 述詞函式的邏輯中使用各項目的索引。Each element's index is used in the logic of the predicate function.

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

根據述詞來篩選值序列。Filters a sequence of values based on a predicate.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TSource> ^ Where(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, bool> ^ predicate);
public static System.Collections.Generic.IEnumerable<TSource> Where<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);
static member Where : seq<'Source> * Func<'Source, bool> -> seq<'Source>
<Extension()>
Public Function Where(Of TSource) (source As IEnumerable(Of TSource), predicate As Func(Of TSource, Boolean)) 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>

要篩選的 IEnumerable<T>An IEnumerable<T> to filter.

predicate
Func<TSource,Boolean>

用來測試每個項目是否符合條件的函式。A function to test each element for a condition.

傳回

IEnumerable<TSource>

IEnumerable<T>,其中包含輸入序列中符合條件的項目。An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.

例外狀況

sourcepredicatenullsource or predicate is null.

範例

下列程式碼範例示範如何使用Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)來篩選序列。The following code example demonstrates how to use Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) to filter a sequence.

List<string> fruits =
    new List<string> { "apple", "passionfruit", "banana", "mango", 
                    "orange", "blueberry", "grape", "strawberry" };

IEnumerable<string> query = fruits.Where(fruit => fruit.Length < 6);

foreach (string fruit in query)
{
    Console.WriteLine(fruit);
}
/*
 This code produces the following output:

 apple
 mango
 grape
*/
' Create a list of strings.
Dim fruits As New List(Of String)(New String() _
                    {"apple", "passionfruit", "banana", "mango",
                     "orange", "blueberry", "grape", "strawberry"})

' Restrict the results to those strings whose 
' length is less than six.
Dim query As IEnumerable(Of String) =
fruits.Where(Function(fruit) fruit.Length < 6)

' Display the results.
Dim output As New System.Text.StringBuilder
For Each fruit As String In query
    output.AppendLine(fruit)
Next
MsgBox(output.ToString())

' This code produces the following output:
'
' apple
' mango
' grape

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. 這個方法所表示的查詢, 必須等到透過直接GetEnumerator呼叫其方法, 或是在 Visual C#或For Each Visual Basic 中使用foreach來列舉物件之後, 才會執行。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.

在查詢運算式語法中, where (Visual C#) 或Where (Visual Basic) 子句會轉譯成的Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)調用。In query expression syntax, a where (Visual C#) or Where (Visual Basic) clause translates to an invocation of Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>).

另請參閱

Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>)

根據述詞來篩選值序列。Filters a sequence of values based on a predicate. 述詞函式的邏輯中使用各項目的索引。Each element's index is used in the logic of the predicate function.

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

要篩選的 IEnumerable<T>An IEnumerable<T> to filter.

predicate
Func<TSource,Int32,Boolean>

用來測試各來源項目是否符合條件的函式;此函式的第二個參數代表來源項目的索引。A function to test each source element for a condition; the second parameter of the function represents the index of the source element.

傳回

IEnumerable<TSource>

IEnumerable<T>,其中包含輸入序列中符合條件的項目。An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.

例外狀況

sourcepredicatenullsource or predicate is null.

範例

下列程式碼範例示範如何使用Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) , 根據包含每個專案索引的述詞來篩選序列。The following code example demonstrates how to use Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>) to filter a sequence based on a predicate that involves the index of each element.

int[] numbers = { 0, 30, 20, 15, 90, 85, 40, 75 };

IEnumerable<int> query =
    numbers.Where((number, index) => number <= index * 10);

foreach (int number in query)
{
    Console.WriteLine(number);
}
/*
 This code produces the following output:

 0
 20
 15
 40
*/
' Create an array of integers.
Dim numbers() As Integer = {0, 30, 20, 15, 90, 85, 40, 75}

' Restrict the results to those numbers whose
' values are less than or equal to their index times 10.
Dim query As IEnumerable(Of Integer) =
numbers.Where(Function(number, index) number <= index * 10)

' Display the results.
Dim output As New System.Text.StringBuilder
For Each number As Integer In query
    output.AppendLine(number)
Next
MsgBox(output.ToString())

' This code produces the following output:
'
' 0
' 20
' 15
' 40

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. 這個方法所表示的查詢, 必須等到透過直接GetEnumerator呼叫其方法, 或是在 Visual C#或For Each Visual Basic 中使用foreach來列舉物件之後, 才會執行。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.

的第一個自predicate變數表示要測試的元素。The first argument of predicate represents the element to test. 第二個引數代表內source元素以零為起始的索引。The second argument represents the zero-based index of the element within source.

適用於