Enumerable.All<TSource> Method

Determines whether all elements of a sequence satisfy a condition.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function All(Of TSource) ( _
    source As IEnumerable(Of TSource), _
    predicate As Func(Of TSource, Boolean) _
) As Boolean
public static bool All<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, bool> predicate
)

Type Parameters

  • TSource
    The type of the elements of source.

Parameters

  • predicate
    Type: System.Func<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.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception Condition
ArgumentNullException

source or predicate is nulla null reference (Nothing in Visual Basic).

Remarks

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<TSource>.

Examples

The following code example demonstrates how to use All<TSource> to determine whether all the elements in a sequence satisfy a condition.

   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(pet) pet.Name.StartsWith("B"))

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

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

      class Pet
      {
         public string Name { get; set; }
         public int Age { get; set; }
      }

      public static void AllEx()
      {
         // Create an array of Pets.
         Pet[] pets = { new Pet { Name="Barley", Age=10 },
                            new Pet { Name="Boots", Age=4 },
                            new Pet { Name="Whiskers", Age=6 } };

         // Determine whether all pet names 
         // in the array start with 'B'.
         bool allStartWithB = pets.All(pet =>
                                           pet.Name.StartsWith("B"));

         outputBlock.Text += String.Format(
             "{0} pet names start with 'B'.",
             allStartWithB ? "All" : "Not all") + "\n";
      }

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

The Boolean value that the All<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 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
      outputBlock.Text &= name & vbCrLf
   Next

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

End Sub
class Pet
{
   public string Name { get; set; }
   public int Age { get; set; }
}
class Person
{
   public string LastName { get; set; }
   public Pet[] Pets { get; set; }
}

public static void AllEx2()
{
   List<Person> people = new List<Person>
           { new Person { LastName = "Haas",
                          Pets = new Pet[] { new Pet { Name="Barley", Age=10 },
                                             new Pet { Name="Boots", Age=14 },
                                             new Pet { Name="Whiskers", Age=6 }}},
             new Person { LastName = "Fakhouri",
                          Pets = new Pet[] { new Pet { Name = "Snowball", Age = 1}}},
             new Person { LastName = "Antebi",
                          Pets = new Pet[] { new Pet { Name = "Belle", Age = 8} }},
             new Person { LastName = "Philips",
                          Pets = new Pet[] { new Pet { Name = "Sweetie", Age = 2},
                                             new Pet { Name = "Rover", Age = 13}} }
           };

   // Determine which people have pets that are all older than 5.
   IEnumerable<string> names = from person in people
                               where person.Pets.All(pet => pet.Age > 5)
                               select person.LastName;

   foreach (string name in names)
   {
      outputBlock.Text += name + "\n";
   }

   /* This code produces the following output:
    * 
    * Haas
    * Antebi
    */
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.