Artikel
11/18/2011

Queryable.SkipWhile<TSource> Method (IQueryable<TSource>, Expression<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 IQueryable(Of TSource), _
    predicate As Expression(Of Func(Of TSource, Boolean)) _
) As IQueryable(Of TSource)

public static IQueryable<TSource> SkipWhile<TSource>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, bool>> predicate
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
An IQueryable<T> to return elements from.

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

Return Value

Type: System.Linq.IQueryable<TSource>
An IQueryable<T> that contains elements from source 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 IQueryable<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 has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T, TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

The SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) method generates a MethodCallExpression that represents calling SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) depends on the implementation of the type of the source parameter. The expected behavior is that it applies predicate to each element in source until it finds an element for which predicate returns false. That element and all the remaining elements are returned.

Examples

The following code example demonstrates how to use SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Boolean>>) to skip elements of an array as long as a condition is true.

      Dim grades() As Integer = {59, 82, 70, 56, 92, 98, 85}

      ' Get all grades less than 80 by first  sorting the grades 
      ' in descending order and then taking all the grades that 
      ' occur after the first grade that is less than 80.
      Dim lowerGrades = grades.AsQueryable() _
          .OrderByDescending(Function(grade) grade) _
          .SkipWhile(Function(grade) grade >= 80)

      Dim output As New System.Text.StringBuilder
      output.AppendLine("All grades below 80:")
      For Each grade As Integer In lowerGrades
         output.AppendLine(grade)
      Next

      ' Display the output.
      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 };

         // Get all grades less than 80 by first
         // sorting the grades in descending order and then
         // taking all the grades after the first grade
         // that is less than 80.
         IEnumerable<int> lowerGrades =
             grades.AsQueryable()
             .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

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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