Enumerable.SkipWhile(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Int32, Boolean))

 

Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. The element's index is used in the logic of the predicate function.

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

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

Parameters

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

An IEnumerable(Of T) to return elements from.

predicate
Type: System.Func(Of 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(Of TSource)

An IEnumerable(Of T) that contains the elements from the input sequence starting at the first element in the linear series that does not pass the test specified by predicate.

Type Parameters

TSource

The type of the elements of source.

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 SkipWhile(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Int32, Boolean)) method tests each element of source by using predicate and skips the element if the result is true. After the predicate function returns false for an element, that element and the remaining elements in source are yielded and there are no more invocations of predicate.

If predicate returns true for all elements in the sequence, an empty IEnumerable(Of T) is returned.

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 Skip While clause translates to an invocation of SkipWhile.

The following code example demonstrates how to use SkipWhile(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Int32, Boolean)) to skip elements of an array as long as a condition that depends on the element's index is true.

' Create an array of integers.
Dim amounts() As Integer = _
    {5000, 2500, 9000, 8000, 6500, 4000, 1500, 5500}

' Skip items in the array whose value is greater than
' the item's index times 1000; get the remaining items.
Dim query As IEnumerable(Of Integer) = _
    amounts.SkipWhile(Function(amount, index) _
                          amount > index * 1000)

' Output the results.
Dim output As New System.Text.StringBuilder
For Each amount As Integer In query
    output.AppendLine(amount)
Next
MsgBox(output.ToString())

' This code produces the following output:
'
' 4000
' 1500
' 5500

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
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