Export (0) Print
Expand All

Enumerable.TakeWhile(TSource) Method (IEnumerable(TSource), Func(TSource, Int32, Boolean))

Returns elements from a sequence as long as a specified condition is true. The element's index is used in the logic of the predicate function.

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

JScript does not support generic types or methods.

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable(TSource)

The sequence to return elements from.

predicate
Type: System.Func(TSource, Int32, Boolean)

A function to test each source element for a condition; the second parameter of the function represents the index of the source element.

Return Value

Type: System.Collections.Generic.IEnumerable(TSource)
An IEnumerable(T) that contains elements from the input sequence that occur before the element at which the test no longer passes.

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 a null reference (Nothing in Visual Basic).

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, Int32, 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 first argument of predicate represents the element to test. The second argument represents the zero-based index of the element within source.

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.

The following code example demonstrates how to use TakeWhile(TSource)(IEnumerable(TSource), Func(TSource, Int32, Boolean)) to return elements from the start of a sequence as long as a condition that uses the element's index is true.

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

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0

Community Additions

ADD
Show:
© 2014 Microsoft