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)
The type of the elements of source
.
source
An IEnumerable<T> to filter.
predicate
A function to test each element for a condition.
An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.
source
or predicate
is null
.
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
Console.WriteLine(output.ToString())
' This code produces the following output:
'
' apple
' mango
' grape
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. 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 C# or For Each
in Visual Basic.
In query expression syntax, a where
(C#) or Where
(Visual Basic) clause translates to an invocation of Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>).
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