Enumerable.First(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Boolean))
Returns the first element in a sequence that satisfies a specified condition.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
'Declaration <ExtensionAttribute> _ Public Shared 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
- Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to return an element from.
- predicate
- Type: System.Func(Of TSource, Boolean)
A function to test each element for a condition.
Return Value
Type: TSourceThe 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(Of TSource). When you use instance method syntax to call this method, omit the first parameter.| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate is Nothing. |
| InvalidOperationException | No element satisfies the condition in predicate. -or- The source sequence is empty. |
The First(Of TSource)(IEnumerable(Of TSource), Func(Of 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(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Boolean)) to return the first element of an array that satisfies a condition.
' 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.
outputBlock.Text &= first & vbCrLf
' This code produces the following output:
'
' 92
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