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

.NET Framework (current version)

Returns elements from a sequence as long as a specified condition is true.

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

Syntax

static member TakeWhile<'TSource> : 
        source:IEnumerable<'TSource> *
        predicate:Func<'TSource, bool> -> IEnumerable<'TSource>

Parameters

source: Type: System.Collections.Generic.IEnumerable<'TSource>
A sequence to return elements from.

predicate: Type: System.Func<'TSource, Boolean>
A function to test each element for a condition.

Return Value

Type: System.Collections.Generic.IEnumerable<'TSource>

An IEnumerable<'T> that contains the elements from the input sequence that occur before the element at which the test no longer passes.

Type Parameters

TSource: The type of the elements of source.

Exceptions

Exception	Condition
ArgumentNullException	source or predicate is null.

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

The TakeWhile<'TSource>(IEnumerable<'TSource>, Func<'TSource, Boolean>) method tests each element of source by using predicate and yields the element if the result is true. Enumeration stops when the predicate function returns false for an element or when source contains no more elements.

The TakeWhile and SkipWhile methods are functional complements. Given a sequence coll and a pure function p, concatenating the results of coll.TakeWhile(p) and coll.SkipWhile(p) yields the same sequence as coll.

In Visual Basic query expression syntax, a Take While clause translates to an invocation of TakeWhile.

Examples

The following code example demonstrates how to use TakeWhile<'TSource>(IEnumerable<'TSource>, Func<'TSource, Boolean>) to return elements from the start of a sequence as long as a condition is true.

No code example is currently available or this language may not be supported.

Version Information

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1