Where(TSource) Method (IEnumerable(TSource), Func(TSource, Boolean))
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Enumerable.Where(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Boolean))

 

Filters a sequence of values based on a predicate.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

<ExtensionAttribute>
Public Shared Function Where(Of TSource) (
	source As IEnumerable(Of TSource),
	predicate As Func(Of TSource, Boolean)
) As IEnumerable(Of TSource)

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)

An IEnumerable(Of T) to filter.

predicate
Type: System.Func(Of TSource, Boolean)

A function to test each element for a condition.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TSource)

An IEnumerable(Of T) that contains elements from the input sequence that satisfy the condition.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source or predicate is null.

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 Visual C# or For Each in Visual Basic.

In query expression syntax, a where (Visual C#) or Where (Visual Basic) clause translates to an invocation of Where(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Boolean)).

The following code example demonstrates how to use Where(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Boolean)) to filter a sequence.

' 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

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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