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Enumerable.All<TSource> Method

Determines whether all elements of a sequence satisfy a condition.

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

public static bool All<TSource>(
	this IEnumerable<TSource> source,
	Func<TSource, bool> predicate
)

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> that contains the elements to apply the predicate to.
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.

ExceptionCondition
ArgumentNullException

source or predicate is null.

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>.

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


      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.


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
    */
}


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

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

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