Enumerable.First Method
Definition
Returns the first element of a sequence.
Overloads
First<TSource>(IEnumerable<TSource>) |
Returns the first element of a sequence. |
First<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) |
Returns the first element in a sequence that satisfies a specified condition. |
First<TSource>(IEnumerable<TSource>)
Returns the first element of a sequence.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static TSource First(System::Collections::Generic::IEnumerable<TSource> ^ source);
public static TSource First<TSource> (this System.Collections.Generic.IEnumerable<TSource> source);
static member First : seq<'Source> -> 'Source
<Extension()>
Public Function First(Of TSource) (source As IEnumerable(Of TSource)) As TSource
Type Parameters
- TSource
The type of the elements of source
.
Parameters
- source
- IEnumerable<TSource>
The IEnumerable<T> to return the first element of.
Returns
- TSource
The first element in the specified sequence.
Exceptions
source
is null
.
The source sequence is empty.
Examples
The following code example demonstrates how to use First<TSource>(IEnumerable<TSource>) to return the first element of an array.
int[] numbers = { 9, 34, 65, 92, 87, 435, 3, 54,
83, 23, 87, 435, 67, 12, 19 };
int first = numbers.First();
Console.WriteLine(first);
/*
This code produces the following output:
9
*/
' Create an array of integers.
Dim numbers() As Integer =
{9, 34, 65, 92, 87, 435, 3, 54, 83, 23, 87, 435, 67, 12, 19}
' Select the first element in the array.
Dim first As Integer = numbers.First()
' Display the output.
Console.WriteLine(first)
' This code produces the following output:
'
' 9
Remarks
The First<TSource>(IEnumerable<TSource>) method throws an exception if source
contains no elements. To instead return a default value when the source sequence is empty, use the FirstOrDefault method.
Applies to
First<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)
Returns the first element in a sequence that satisfies a specified condition.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static TSource First(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, bool> ^ predicate);
public static TSource First<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);
static member First : seq<'Source> * Func<'Source, bool> -> 'Source
<Extension()>
Public Function First(Of TSource) (source As IEnumerable(Of TSource), predicate As Func(Of TSource, Boolean)) As TSource
Type Parameters
- TSource
The type of the elements of source
.
Parameters
- source
- IEnumerable<TSource>
An IEnumerable<T> to return an element from.
Returns
- TSource
The first element in the sequence that passes the test in the specified predicate function.
Exceptions
source
or predicate
is null
.
No element satisfies the condition in predicate
.
-or-
The source sequence is empty.
Examples
The following code example demonstrates how to use First<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) to return the first element of an array that satisfies a condition.
int[] numbers = { 9, 34, 65, 92, 87, 435, 3, 54,
83, 23, 87, 435, 67, 12, 19 };
int first = numbers.First(number => number > 80);
Console.WriteLine(first);
/*
This code produces the following output:
92
*/
' Create an array of integers.
Dim numbers() As Integer =
{9, 34, 65, 92, 87, 435, 3, 54, 83, 23, 87, 435, 67, 12, 19}
' Select the first element in the array whose value is greater than 80.
Dim first As Integer = numbers.First(Function(number) number > 80)
' Display the output.
Console.WriteLine(first)
' This code produces the following output:
'
' 92
Remarks
The First<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) method throws an exception if no matching element is found in source
. To instead return a default value when no matching element is found, use the FirstOrDefault method.