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

 

Determines whether all elements of a sequence satisfy a condition.

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

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

Parameters

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

An IEnumerable(Of T) that contains the elements to apply the predicate to.

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

A function to test each element for a condition.

Return Value

Type: System.Boolean

true if every element of the source sequence passes the test in the specified predicate, or if the sequence is empty; otherwise, false.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source or predicate is null.

System_CAPS_noteNote

This method does not return all the elements of a collection. Instead, it determines whether all the elements of a collection satisfy a condition.

The enumeration of source is stopped as soon as the result can be determined.

In Visual Basic query expression syntax, an Aggregate Into All() clause translates to an invocation of All(Of TSource).

The following code example demonstrates how to use All(Of TSource) to determine whether all the elements in a sequence satisfy a condition. Variable allStartWithB is true if all the pet names start with "B" or if the pets array is empty.

Structure Pet
    Public Name As String
    Public Age As Integer
End Structure

Sub AllEx()
    ' Create an array of Pets.
    Dim pets() As Pet = _
        {New Pet With {.Name = "Barley", .Age = 2}, _
         New Pet With {.Name = "Boots", .Age = 4}, _
         New Pet With {.Name = "Whiskers", .Age = 7}}

    ' Determine whether all pet names in the array start with "B".
    Dim allNames As Boolean = _
        pets.All(Function(ByVal pet) pet.Name.StartsWith("B"))

    ' Display the output.
    Dim text As String = IIf(allNames, "All", "Not all")
    MsgBox(text & " pet names start with 'B'.")
End Sub

' This code produces the following output:
'
' Not all pet names start with 'B'.

The Boolean value that the All(Of TSource) method returns is typically used in the predicate of a where clause (Where clause in Visual Basic) or a direct call to the Where(Of TSource) method. The following example demonstrates this use of the All method.

Structure Pet
    Public Name As String
    Public Age As Integer
End Structure

Structure Person
    Public LastName As String
    Public Pets() As Pet
End Structure

Sub AllEx2()
    Dim people As New List(Of Person)(New Person() _
        {New Person With {.LastName = "Haas", _
                          .Pets = New Pet() {New Pet With {.Name = "Barley", .Age = 10}, _
                                             New Pet With {.Name = "Boots", .Age = 14}, _
                                             New Pet With {.Name = "Whiskers", .Age = 6}}}, _
          New Person With {.LastName = "Fakhouri", _
                           .Pets = New Pet() {New Pet With {.Name = "Snowball", .Age = 1}}}, _
          New Person With {.LastName = "Antebi", _
                           .Pets = New Pet() {New Pet With {.Name = "Belle", .Age = 8}}}, _
          New Person With {.LastName = "Philips", _
                           .Pets = New Pet() {New Pet With {.Name = "Sweetie", .Age = 2}, _
                                              New Pet With {.Name = "Rover", .Age = 13}}}})

    ' Determine which people have pets that are all older than 5.
    Dim names = From person In people _
                Where person.Pets.All(Function(pet) pet.Age > 5) _
                Select person.LastName

    For Each name As String In names
        Console.WriteLine(name)
    Next

    ' This code produces the following output:
    '
    ' Haas
    ' Antebi

End Sub

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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