Enumerable.SkipWhile<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)
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Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function SkipWhile(Of TSource) ( _
source As IEnumerable(Of TSource), _
predicate As Func(Of TSource, Boolean) _
) As IEnumerable(Of TSource)
public static IEnumerable<TSource> SkipWhile<TSource>(
this IEnumerable<TSource> source,
Func<TSource, bool> predicate
)
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> 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 starting at the first element in the linear series that does not pass the test specified by predicate.
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.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate is nulla null reference (Nothing in Visual Basic). |
Remarks
The SkipWhile<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) 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.
This 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<T> is returned.
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.
Examples
The following code example demonstrates how to use SkipWhile<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) to skip elements of an array as long as a condition is true.
' Create an array of integers that represent grades.
Dim grades() As Integer = {59, 82, 70, 56, 92, 98, 85}
' Sort the grades in descending order and
' get all grades greater less than 80.
Dim lowerGrades As IEnumerable(Of Integer) = _
grades _
.OrderByDescending(Function(grade) grade) _
.SkipWhile(Function(grade) grade >= 80)
' Display the results.
Dim output As New System.Text.StringBuilder("All grades below 80:" & vbCrLf)
For Each grade As Integer In lowerGrades
output.AppendLine(grade)
Next
outputBlock.Text &= output.ToString() & vbCrLf
' This code produces the following output:
'
' All grades below 80:
' 70
' 59
' 56
int[] grades = { 59, 82, 70, 56, 92, 98, 85 };
IEnumerable<int> lowerGrades =
grades
.OrderByDescending(grade => grade)
.SkipWhile(grade => grade >= 80);
outputBlock.Text += "All grades below 80:" + "\n";
foreach (int grade in lowerGrades)
{
outputBlock.Text += grade + "\n";
}
/*
This code produces the following output:
All grades below 80:
70
59
56
*/
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.