MoreEnumerable.TakeUntil(TSource) Method

MoreEnumerableTakeUntilTSource Method

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.

Namespace: MoreLinq
Assembly: MoreLinq (in MoreLinq.dll) Version: 2.0.0

Syntax

C++

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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
)

[<ExtensionAttribute>]
static member TakeUntil : 
        source : IEnumerable<'TSource> * 
        predicate : Func<'TSource, bool> -> IEnumerable<'TSource>

Parameters

source: Type: System.Collections.GenericIEnumerableTSource
Source sequence
predicate: Type: SystemFuncTSource, Boolean
Predicate used to determine when to stop yielding results from the source.

Type Parameters

TSource: Type of the source sequence

Return Value

Type: IEnumerableTSource
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 IEnumerableTSource. 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).

Exceptions

Exception	Condition
ArgumentNullException	source or predicate is null

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

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{ 1, 2, 3, 4, 5 }

and with a predicate of

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x => x == 3

, the result would be

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{ 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.)

Reference

MoreEnumerable Class

MoreLinq Namespace