Enumerable.First Method (System.Linq) (original) (raw)

Source:

First.cs

Source:

First.cs

Source:

First.cs

Source:

First.cs

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

predicate

Func<TSource,Boolean>

A function to test each element for a condition.

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(IEnumerable, 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(IEnumerable, 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.

Applies to