List<T>.Remove(T) Method

Definition

Namespace:: System.Collections.Generic

Assemblies:: mscorlib.dll, System.Collections.dll

Assemblies:: netstandard.dll, System.Collections.dll

Assembly:: System.Collections.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

Source:: List.cs

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Removes the first occurrence of a specific object from the List<T>.

public:
 virtual bool Remove(T item);

public bool Remove(T item);

abstract member Remove : 'T -> bool
override this.Remove : 'T -> bool

Public Function Remove (item As T) As Boolean

Parameters

item: T

The object to remove from the List<T>. The value can be null for reference types.

Returns

Boolean

true if item is successfully removed; otherwise, false. This method also returns false if item was not found in the List<T>.

Implements

Remove(T)

Examples

The following example demonstrates how to add, remove, and insert a simple business object in a List<T>.

using System;
using System.Collections.Generic;
// Simple business object. A PartId is used to identify the type of part
// but the part name can change.
public class Part : IEquatable<Part>
 {
 public string PartName { get; set; }

 public int PartId { get; set; }

 public override string ToString()
 {
 return "ID: " + PartId + " Name: " + PartName;
 }
 public override bool Equals(object obj)
 {
 if (obj == null) return false;
 Part objAsPart = obj as Part;
 if (objAsPart == null) return false;
 else return Equals(objAsPart);
 }
 public override int GetHashCode()
 {
 return PartId;
 }
 public bool Equals(Part other)
 {
 if (other == null) return false;
 return (this.PartId.Equals(other.PartId));
 }
 // Should also override == and != operators.
 }
public class Example
{
 public static void Main()
 {
 // Create a list of parts.
 List<Part> parts = new List<Part>();

 // Add parts to the list.
 parts.Add(new Part() { PartName = "crank arm", PartId = 1234 });
 parts.Add(new Part() { PartName = "chain ring", PartId = 1334 });
 parts.Add(new Part() { PartName = "regular seat", PartId = 1434 });
 parts.Add(new Part() { PartName = "banana seat", PartId = 1444 });
 parts.Add(new Part() { PartName = "cassette", PartId = 1534 });
 parts.Add(new Part() { PartName = "shift lever", PartId = 1634 });

 // Write out the parts in the list. This will call the overridden ToString method
 // in the Part class.
 Console.WriteLine();
 foreach (Part aPart in parts)
 {
 Console.WriteLine(aPart);
 }

 // Check the list for part #1734. This calls the IEquatable.Equals method
 // of the Part class, which checks the PartId for equality.
 Console.WriteLine("\nContains(\"1734\"): {0}",
 parts.Contains(new Part { PartId = 1734, PartName = "" }));

 // Insert a new item at position 2.
 Console.WriteLine("\nInsert(2, \"1834\")");
 parts.Insert(2, new Part() { PartName = "brake lever", PartId = 1834 });

 //Console.WriteLine();
 foreach (Part aPart in parts)
 {
 Console.WriteLine(aPart);
 }

 Console.WriteLine("\nParts[3]: {0}", parts[3]);

 Console.WriteLine("\nRemove(\"1534\")");

 // This will remove part 1534 even though the PartName is different,
 // because the Equals method only checks PartId for equality.
 parts.Remove(new Part() { PartId = 1534, PartName = "cogs" });

 Console.WriteLine();
 foreach (Part aPart in parts)
 {
 Console.WriteLine(aPart);
 }
 Console.WriteLine("\nRemoveAt(3)");
 // This will remove the part at index 3.
 parts.RemoveAt(3);

 Console.WriteLine();
 foreach (Part aPart in parts)
 {
 Console.WriteLine(aPart);
 }

 /*

 ID: 1234 Name: crank arm
 ID: 1334 Name: chain ring
 ID: 1434 Name: regular seat
 ID: 1444 Name: banana seat
 ID: 1534 Name: cassette
 ID: 1634 Name: shift lever

 Contains("1734"): False

 Insert(2, "1834")
 ID: 1234 Name: crank arm
 ID: 1334 Name: chain ring
 ID: 1834 Name: brake lever
 ID: 1434 Name: regular seat
 ID: 1444 Name: banana seat
 ID: 1534 Name: cassette
 ID: 1634 Name: shift lever

 Parts[3]: ID: 1434 Name: regular seat

 Remove("1534")

 ID: 1234 Name: crank arm
 ID: 1334 Name: chain ring
 ID: 1834 Name: brake lever
 ID: 1434 Name: regular seat
 ID: 1444 Name: banana seat
 ID: 1634 Name: shift lever

 RemoveAt(3)

 ID: 1234 Name: crank arm
 ID: 1334 Name: chain ring
 ID: 1834 Name: brake lever
 ID: 1444 Name: banana seat
 ID: 1634 Name: shift lever


 */
 }
}

Imports System.Collections.Generic

' Simple business object. A PartId is used to identify the type of part 
' but the part name can change. 
Public Class Part
 Implements IEquatable(Of Part)
 Public Property PartName() As String
 Get
 Return m_PartName
 End Get
 Set(value As String)
 m_PartName = Value
 End Set
 End Property
 Private m_PartName As String

 Public Property PartId() As Integer
 Get
 Return m_PartId
 End Get
 Set(value As Integer)
 m_PartId = Value
 End Set
 End Property
 Private m_PartId As Integer

 Public Overrides Function ToString() As String
 Return "ID: " & PartId & " Name: " & PartName
 End Function
 Public Overrides Function Equals(obj As Object) As Boolean
 If obj Is Nothing Then
 Return False
 End If
 Dim objAsPart As Part = TryCast(obj, Part)
 If objAsPart Is Nothing Then
 Return False
 Else
 Return Equals(objAsPart)
 End If
 End Function
 Public Overrides Function GetHashCode() As Integer
 Return PartId
 End Function
 Public Overloads Function Equals(other As Part) As Boolean _
 Implements IEquatable(Of Part).Equals
 If other Is Nothing Then
 Return False
 End If
 Return (Me.PartId.Equals(other.PartId))
 End Function
 ' Should also override == and != operators.

End Class
Public Class Example
 Public Shared Sub Main()
 ' Create a list of parts.
 Dim parts As New List(Of Part)()

 ' Add parts to the list.
 parts.Add(New Part() With { _
 .PartName = "crank arm", _
 .PartId = 1234 _
 })
 parts.Add(New Part() With { _
 .PartName = "chain ring", _
 .PartId = 1334 _
 })
 parts.Add(New Part() With { _
 .PartName = "regular seat", _
 .PartId = 1434 _
 })
 parts.Add(New Part() With { _
 .PartName = "banana seat", _
 .PartId = 1444 _
 })
 parts.Add(New Part() With { _
 .PartName = "cassette", _
 .PartId = 1534 _
 })
 parts.Add(New Part() With { _
 .PartName = "shift lever", _
 .PartId = 1634 _
 })



 ' Write out the parts in the list. This will call the overridden ToString method
 ' in the Part class.
 Console.WriteLine()
 For Each aPart As Part In parts
 Console.WriteLine(aPart)
 Next


 ' Check the list for part #1734. This calls the IEquatable.Equals method
 ' of the Part class, which checks the PartId for equality.
 Console.WriteLine(vbLf & "Contains(""1734""): {0}", parts.Contains(New Part() With { _
 .PartId = 1734, _
 .PartName = "" _
 }))

 ' Insert a new item at position 2.
 Console.WriteLine(vbLf & "Insert(2, ""1834"")")
 parts.Insert(2, New Part() With { _
 .PartName = "brake lever", _
 .PartId = 1834 _
 })


 'Console.WriteLine();
 For Each aPart As Part In parts
 Console.WriteLine(aPart)
 Next

 Console.WriteLine(vbLf & "Parts[3]: {0}", parts(3))

 Console.WriteLine(vbLf & "Remove(""1534"")")

 ' This will remove part 1534 even though the PartName is different,
 ' because the Equals method only checks PartId for equality.
 parts.Remove(New Part() With { _
 .PartId = 1534, _
 .PartName = "cogs" _
 })

 Console.WriteLine()
 For Each aPart As Part In parts
 Console.WriteLine(aPart)
 Next

 Console.WriteLine(vbLf & "RemoveAt(3)")
 ' This will remove part at index 3.
 parts.RemoveAt(3)

 Console.WriteLine()
 For Each aPart As Part In parts
 Console.WriteLine(aPart)
 Next
 End Sub
 '
 ' This example code produces the following output:
 ' ID: 1234 Name: crank arm
 ' ID: 1334 Name: chain ring
 ' ID: 1434 Name: regular seat
 ' ID: 1444 Name: banana seat
 ' ID: 1534 Name: cassette
 ' ID: 1634 Name: shift lever
 '
 ' Contains("1734"): False
 '
 ' Insert(2, "1834")
 ' ID: 1234 Name: crank arm
 ' ID: 1334 Name: chain ring
 ' ID: 1834 Name: brake lever
 ' ID: 1434 Name: regular seat
 ' ID: 1444 Name: banana seat
 ' ID: 1534 Name: cassette
 ' ID: 1634 Name: shift lever
 '
 ' Parts[3]: ID: 1434 Name: regular seat
 '
 ' Remove("1534")
 '
 ' ID: 1234 Name: crank arm
 ' ID: 1334 Name: chain ring
 ' ID: 1834 Name: brake lever
 ' ID: 1434 Name: regular seat
 ' ID: 1444 Name: banana seat
 ' ID: 1634 Name: shift lever
 ' '
 ' RemoveAt(3)
 '
 ' ID: 1234 Name: crank arm
 ' ID: 1334 Name: chain ring
 ' ID: 1834 Name: brake lever
 ' ID: 1444 Name: banana seat
 ' ID: 1634 Name: shift lever
 ' 

End Class


// Simple business object. A PartId is used to identify the type of part 
// but the part name can change. 
[<CustomEquality; NoComparison>]
type Part = { PartId : int ; mutable PartName : string } with
 override this.GetHashCode() = hash this.PartId
 override this.Equals(other) =
 match other with
 | :? Part as p -> this.PartId = p.PartId
 | _ -> false
 override this.ToString() = sprintf "ID: %i Name: %s" this.PartId this.PartName

[<EntryPoint>]
let main argv = 
 // We refer to System.Collections.Generic.List<'T> by its type 
 // abbreviation ResizeArray<'T> to avoid conflicts with the F# List module. 
 // Note: In F# code, F# linked lists are usually preferred over
 // ResizeArray<'T> when an extendable collection is required.
 let parts = ResizeArray<_>()
 parts.Add({PartName = "crank arm" ; PartId = 1234})
 parts.Add({PartName = "chain ring"; PartId = 1334 })
 parts.Add({PartName = "regular seat"; PartId = 1434 })
 parts.Add({PartName = "banana seat"; PartId = 1444 })
 parts.Add({PartName = "cassette"; PartId = 1534 })
 parts.Add({PartName = "shift lever"; PartId = 1634 })

 // Write out the parts in the ResizeArray. This will call the overridden ToString method
 // in the Part type
 printfn ""
 parts |> Seq.iter (fun p -> printfn "%O" p)

 // Check the ResizeArray for part #1734. This calls the IEquatable.Equals method 
 // of the Part type, which checks the PartId for equality. 
 printfn "\nContains(\"1734\"): %b" (parts.Contains({PartId=1734; PartName=""}))
 
 // Insert a new item at position 2.
 printfn "\nInsert(2, \"1834\")"
 parts.Insert(2, { PartName = "brake lever"; PartId = 1834 })

 // Write out all parts
 parts |> Seq.iter (fun p -> printfn "%O" p)

 printfn "\nParts[3]: %O" parts.[3]

 printfn "\nRemove(\"1534\")"
 // This will remove part 1534 even though the PartName is different, 
 // because the Equals method only checks PartId for equality.
 // Since Remove returns true or false, we need to ignore the result
 parts.Remove({PartId=1534; PartName="cogs"}) |> ignore

 // Write out all parts
 printfn ""
 parts |> Seq.iter (fun p -> printfn "%O" p)

 printfn "\nRemoveAt(3)"
 // This will remove the part at index 3.
 parts.RemoveAt(3)

 // Write out all parts
 printfn ""
 parts |> Seq.iter (fun p -> printfn "%O" p)

 0 // return an integer exit code

The following example demonstrates Remove method. Several properties and methods of the List<T> generic class are used to add, insert, and search the list. After these operations, the list contains a duplicate. The Remove method is used to remove the first instance of the duplicate item, and the contents are displayed. The Remove method always removes the first instance it encounters.

List<string> dinosaurs = new List<string>();

Console.WriteLine("\nCapacity: {0}", dinosaurs.Capacity);

dinosaurs.Add("Tyrannosaurus");
dinosaurs.Add("Amargasaurus");
dinosaurs.Add("Mamenchisaurus");
dinosaurs.Add("Deinonychus");
dinosaurs.Add("Compsognathus");
Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
 Console.WriteLine(dinosaur);
}

Console.WriteLine("\nCapacity: {0}", dinosaurs.Capacity);
Console.WriteLine("Count: {0}", dinosaurs.Count);

Console.WriteLine("\nContains(\"Deinonychus\"): {0}",
 dinosaurs.Contains("Deinonychus"));

Console.WriteLine("\nInsert(2, \"Compsognathus\")");
dinosaurs.Insert(2, "Compsognathus");

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
 Console.WriteLine(dinosaur);
}

// Shows accessing the list using the Item property.
Console.WriteLine("\ndinosaurs[3]: {0}", dinosaurs[3]);

Console.WriteLine("\nRemove(\"Compsognathus\")");
dinosaurs.Remove("Compsognathus");

Console.WriteLine();
foreach(string dinosaur in dinosaurs)
{
 Console.WriteLine(dinosaur);
}

dinosaurs.TrimExcess();
Console.WriteLine("\nTrimExcess()");
Console.WriteLine("Capacity: {0}", dinosaurs.Capacity);
Console.WriteLine("Count: {0}", dinosaurs.Count);

dinosaurs.Clear();
Console.WriteLine("\nClear()");
Console.WriteLine("Capacity: {0}", dinosaurs.Capacity);
Console.WriteLine("Count: {0}", dinosaurs.Count);

/* This code example produces the following output:

Capacity: 0

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus
Compsognathus

Capacity: 8
Count: 5

Contains("Deinonychus"): True

Insert(2, "Compsognathus")

Tyrannosaurus
Amargasaurus
Compsognathus
Mamenchisaurus
Deinonychus
Compsognathus

dinosaurs[3]: Mamenchisaurus

Remove("Compsognathus")

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus
Compsognathus

TrimExcess()
Capacity: 5
Count: 5

Clear()
Capacity: 5
Count: 0
 */

Imports System.Collections.Generic

Partial Public Class Program
 Public Shared Sub ShowPlanets()
 Dim planets As New List(Of String)

 Console.WriteLine(vbLf & "Capacity: {0}", planets.Capacity)

 planets.Add("Mercury")
 planets.Add("Venus")
 planets.Add("Earth")
 planets.Add("Mars")
 planets.Add("Jupiter")

 Console.WriteLine()
 For Each planet As String In planets
 Console.WriteLine(planet)
 Next

 Console.WriteLine(vbLf & "Capacity: {0}", planets.Capacity)
 Console.WriteLine("Count: {0}", planets.Count)

 Console.WriteLine(vbLf & "Contains(""Mars""): {0}", _
 planets.Contains("Mars"))

 Console.WriteLine(vbLf & "Insert(2, ""Saturn"")")
 planets.Insert(2, "Saturn")

 Console.WriteLine()
 For Each planet As String In planets
 Console.WriteLine(planet)
 Next
 ' Shows how to access the list using the Item property.
 Console.WriteLine(vbLf & "planets(3): {0}", planets(3))
 Console.WriteLine(vbLf & "Remove(""Jupiter"")")
 planets.Remove("Jupiter")

 Console.WriteLine()
 For Each planet As String In planets
 Console.WriteLine(planet)
 Next

 planets.TrimExcess()
 Console.WriteLine(vbLf & "TrimExcess()")
 Console.WriteLine("Capacity: {0}", planets.Capacity)
 Console.WriteLine("Count: {0}", planets.Count)

 planets.Clear()
 Console.WriteLine(vbLf & "Clear()")
 Console.WriteLine("Capacity: {0}", planets.Capacity)
 Console.WriteLine("Count: {0}", planets.Count)
 End Sub
End Class

' This code example produces the following output:
'
' Capacity: 0
'
' Mercury
' Venus
' Earth
' Mars
' Jupiter
'
' Capacity: 8
' Count: 5
'
' Contains("Mars"): True
'
' Insert(2, "Saturn")
'
' Mercury
' Venus
' Saturn
' Earth
' Mars
' Jupiter
'
' planets(3): Earth
'
' Remove("Jupiter")
'
' Mercury
' Venus
' Saturn
' Earth
' Mars
'
' TrimExcess()
' Capacity: 5
' Count: 5
'
' Clear()
' Capacity: 5
' Count: 0


[<EntryPoint>]
let main argv = 
 // We refer to System.Collections.Generic.List<'T> by its type 
 // abbreviation ResizeArray<'T> to avoid conflict with the List module. 
 // Note: In F# code, F# linked lists are usually preferred over
 // ResizeArray<'T> when an extendable collection is required.
 let dinosaurs = ResizeArray<_>()
 
 // Write out the dinosaurs in the ResizeArray.
 let printDinosaurs() =
 printfn ""
 dinosaurs |> Seq.iter (fun p -> printfn "%O" p) 
 
 
 printfn "\nCapacity: %i" dinosaurs.Capacity
 
 dinosaurs.Add("Tyrannosaurus")
 dinosaurs.Add("Amargasaurus")
 dinosaurs.Add("Mamenchisaurus")
 dinosaurs.Add("Deinonychus")
 dinosaurs.Add("Compsognathus")
 
 printDinosaurs()
 
 printfn "\nCapacity: %i" dinosaurs.Capacity
 printfn "Count: %i" dinosaurs.Count
 
 printfn "\nContains(\"Deinonychus\"): %b" (dinosaurs.Contains("Deinonychus"))
 
 printfn "\nInsert(2, \"Compsognathus\")"
 dinosaurs.Insert(2, "Compsognathus")
 
 printDinosaurs()
 
 // Shows accessing the list using the Item property.
 printfn "\ndinosaurs[3]: %s" dinosaurs.[3]
 
 printfn "\nRemove(\"Compsognathus\")"
 dinosaurs.Remove("Compsognathus") |> ignore
 
 printDinosaurs()
 
 dinosaurs.TrimExcess()
 printfn "\nTrimExcess()"
 printfn "Capacity: %i" dinosaurs.Capacity
 printfn "Count: %i" dinosaurs.Count
 
 dinosaurs.Clear()
 printfn "\nClear()"
 printfn "Capacity: %i" dinosaurs.Capacity
 printfn "Count: %i" dinosaurs.Count
 
 0 // return an integer exit code
 
 (* This code example produces the following output:
 
Capacity: 0
 
Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus
Compsognathus
 
Capacity: 8
Count: 5
 
Contains("Deinonychus"): true
 
Insert(2, "Compsognathus")
 
Tyrannosaurus
Amargasaurus
Compsognathus
Mamenchisaurus
Deinonychus
Compsognathus
 
dinosaurs[3]: Mamenchisaurus
 
Remove("Compsognathus")
 
Tyrannosaurus
Amargasaurus
Mamenchisaurus
Deinonychus
Compsognathus
 
TrimExcess()
Capacity: 5
Count: 5
 
Clear()
Capacity: 5
Count: 0
 *)

Remarks

This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.

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

Applies to

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URL: https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1.remove?view=netframework-4.7.2