Enumerable.First<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)

Returns the first element in a sequence that satisfies a specified condition.

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

public static TSource First<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> to return an element from.
predicate
Type: System.Func<TSource, Boolean>
A function to test each element for a condition.

Return Value

Type: TSource
The first element in the sequence that passes the test in the specified predicate function.

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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
ArgumentNullException

source or predicate is null.

InvalidOperationException

No element satisfies the condition in predicate.

-or-

The source sequence is empty.

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.

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
            */



.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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