Enumerable.All<TSource> Method
Definition
Important
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Determines whether all elements of a sequence satisfy a condition.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static bool All(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, bool> ^ predicate);public static bool All<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);static member All : seq<'Source> * Func<'Source, bool> -> bool<Extension()>
Public Function All(Of TSource) (source As IEnumerable(Of TSource), predicate As Func(Of TSource, Boolean)) As BooleanType Parameters
- TSource
The type of the elements of source.
Parameters
- source
- IEnumerable<TSource>
An IEnumerable<T> that contains the elements to apply the predicate to.
Returns
true if every element of the source sequence passes the test in the specified predicate, or if the sequence is empty; otherwise, false.
Exceptions
source or predicate is null.
Examples
The following code example demonstrates how to use All 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.
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"));
Console.WriteLine(
"{0} pet names start with 'B'.",
allStartWithB ? "All" : "Not all");
}
// This code produces the following output:
//
// Not all pet names start with 'B'.
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")
Console.WriteLine($"{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 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)
{
Console.WriteLine(name);
}
/* This code produces the following output:
*
* Haas
* Antebi
*/
}
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
Remarks
Note
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.
