TakeUntil Method (source, predicate)

Returns items from the input sequence until the given predicate returns true when applied to the current source item; that item will be the last returned.

Declaration Syntax

Visual Basic

Visual C++

public static IEnumerable<TSource> TakeUntil<TSource>(
	this IEnumerable<TSource> source,
	Func<TSource, bool> predicate
)

<ExtensionAttribute> _
Public Shared Function TakeUntil(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	predicate As Func(Of TSource, Boolean) _
) As IEnumerable(Of TSource)

public:
[ExtensionAttribute]
generic<typename TSource>
static IEnumerable<TSource>^ TakeUntil(
	IEnumerable<TSource>^ source, 
	Func<TSource, bool>^ predicate
)

Generic Template Parameters

TSource: Type of the source sequence

Parameters

source (IEnumerable<(Of <(<'TSource>)>)>): Source sequence

predicate (Func<(Of <(<'TSource, Boolean>)>)>): Predicate used to determine when to stop yielding results from the source.

Return Value

Items from the source sequence, until the predicate returns true when applied to the item.

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.

Remarks

TakeUntil differs from Enumerable.TakeWhile in two respects. Firstly, the sense of the predicate is reversed: it is expected that the predicate will return false to start with, and then return true - for example, when trying to find a matching item in a sequence.

Secondly, TakeUntil yields the element which causes the predicate to return true. For example, in a sequence

	Copy
{ 1, 2, 3, 4, 5 }

and with a predicate of

	Copy
x => x == 3

, the result would be

	Copy
{ 1, 2, 3 }

TakeUntil is as lazy as possible: it will not iterate over the source sequence until it has to, it won't iterate further than it has to, and it won't evaluate the predicate until it has to. (This means that an item may be returned which would actually cause the predicate to throw an exception if it were evaluated, so long as no more items of data are requested.)

Exceptions

Exception	Condition
ArgumentNullException	source or predicate is null

Assembly: MoreLinq (Module: MoreLinq.dll) Version: 1.0.16006.0 (1.0.16006.1845)