Export (0) Print
Expand All

List(Of T).RemoveAll Method

Removes all the elements that match the conditions defined by the specified predicate.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

Public Function RemoveAll ( _
	match As Predicate(Of T) _
) As Integer


Type: System.Predicate(Of T)

The Predicate(Of T) delegate that defines the conditions of the elements to remove.

Return Value

Type: System.Int32
The number of elements removed from the List(Of T) .


match is Nothing.

The Predicate(Of T) is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of the current List(Of T) are individually passed to the Predicate(Of T) delegate, and the elements that match the conditions are removed from the List(Of T).

This method performs a linear search; therefore, this method is an O(n) operation, where n is Count.

The following example demonstrates the RemoveAll method and several other methods that use the Predicate(Of T) generic delegate.

A List(Of T) of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". The example also defines a search predicate method named EndsWithSaurus, which accepts a string parameter and returns a Boolean value indicating whether the input string ends in "saurus".

The Find, FindLast, and FindAll methods are used to search the list with the search predicate method.

The RemoveAll method is used to remove all entries ending with "saurus". It traverses the list from the beginning, passing each element in turn to the EndsWithSaurus method. The element is removed if the EndsWithSaurus method returns true.


In C# and Visual Basic, it is not necessary to create the Predicate<string> delegate (Predicate(Of String) in Visual Basic) explicitly. These languages infer the correct delegate from context, and create it automatically.

Finally, the Exists method verifies that there are no strings in the list that end with "saurus".

Imports System
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main()

        Dim dinosaurs As New List(Of String)


        For Each dinosaur As String In dinosaurs

        Console.WriteLine(vbLf & _
            "TrueForAll(AddressOf EndsWithSaurus: {0}", _
            dinosaurs.TrueForAll(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "Find(AddressOf EndsWithSaurus): {0}", _
            dinosaurs.Find(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "FindLast(AddressOf EndsWithSaurus): {0}", _
            dinosaurs.FindLast(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & _
            "FindAll(AddressOf EndsWithSaurus):")
        Dim sublist As List(Of String) = _
            dinosaurs.FindAll(AddressOf EndsWithSaurus)

        For Each dinosaur As String In sublist

        Console.WriteLine(vbLf & _
            "{0} elements removed by RemoveAll(AddressOf EndsWithSaurus).", _
            dinosaurs.RemoveAll(AddressOf EndsWithSaurus))

        Console.WriteLine(vbLf & "List now contains:")
        For Each dinosaur As String In dinosaurs

        Console.WriteLine(vbLf & _
            "Exists(AddressOf EndsWithSaurus): {0}", _
            dinosaurs.Exists(AddressOf EndsWithSaurus))

    End Sub 

    ' Search predicate returns true if a string ends in "saurus". 
    Private Shared Function EndsWithSaurus(ByVal s As String) _
        As Boolean 

        Return s.ToLower().EndsWith("saurus")
    End Function 
End Class 

' This code example produces the following output: 


'TrueForAll(AddressOf EndsWithSaurus: False 

'Find(AddressOf EndsWithSaurus): Amargasaurus 

'FindLast(AddressOf EndsWithSaurus): Dilophosaurus 

'FindAll(AddressOf EndsWithSaurus): 

'2 elements removed by RemoveAll(AddressOf EndsWithSaurus). 

'List now contains: 

'Exists(AddressOf EndsWithSaurus): False

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
© 2015 Microsoft