Share via

  • Article

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

Microsoft Silverlight will reach end of support after October 2021. Learn more.

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)

Syntax

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

public static IEnumerable<TSource> SkipWhile<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, int, bool> predicate
)

Type Parameters

  • TSource
    The type of the elements of source.

Parameters

  • 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 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

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<TSource>(IEnumerable<TSource>, Func<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<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.

Examples

The following code example demonstrates how to use SkipWhile<TSource>(IEnumerable<TSource>, Func<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
      outputBlock.Text &= output.ToString() & vbCrLf

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


      int[] amounts = { 5000, 2500, 9000, 8000, 
                             6500, 4000, 1500, 5500 };

      IEnumerable<int> query =
          amounts.SkipWhile((amount, index) => amount > index * 1000);

      foreach (int amount in query)
      {
         outputBlock.Text += amount + "\n";
      }

      /*
       This code produces the following output:

       4000
       1500
       5500
      */

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.