List<T>.Remove(T) Method (System.Collections.Generic) (2023)

Table of Contents
Examples Remarks Applies to See also

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 -> booloverride this.Remove : 'T -> bool
Public Function Remove (item As T) As Boolean

Parameters

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

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 ClassPublic 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.

using namespace System;using namespace System::Collections::Generic;void main(){ List<String^>^ dinosaurs = gcnew 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(); for each(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(); for each(String^ dinosaur in dinosaurs ) { Console::WriteLine(dinosaur); } Console::WriteLine("\ndinosaurs[3]: {0}", dinosaurs[3]); Console::WriteLine("\nRemove(\"Compsognathus\")"); dinosaurs->Remove("Compsognathus"); Console::WriteLine(); for each(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: 0TyrannosaurusAmargasaurusMamenchisaurusDeinonychusCompsognathusCapacity: 8Count: 5Contains("Deinonychus"): TrueInsert(2, "Compsognathus")TyrannosaurusAmargasaurusCompsognathusMamenchisaurusDeinonychusCompsognathusdinosaurs[3]: MamenchisaurusRemove("Compsognathus")TyrannosaurusAmargasaurusMamenchisaurusDeinonychusCompsognathusTrimExcess()Capacity: 5Count: 5Clear()Capacity: 5Count: 0 */
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: 0TyrannosaurusAmargasaurusMamenchisaurusDeinonychusCompsognathusCapacity: 8Count: 5Contains("Deinonychus"): TrueInsert(2, "Compsognathus")TyrannosaurusAmargasaurusCompsognathusMamenchisaurusDeinonychusCompsognathusdinosaurs[3]: MamenchisaurusRemove("Compsognathus")TyrannosaurusAmargasaurusMamenchisaurusDeinonychusCompsognathusTrimExcess()Capacity: 5Count: 5Clear()Capacity: 5Count: 0 */
Imports System.Collections.GenericPublic Class Example Public Shared Sub Main() Dim dinosaurs As New List(Of String) Console.WriteLine(vbLf & "Capacity: {0}", dinosaurs.Capacity) dinosaurs.Add("Tyrannosaurus") dinosaurs.Add("Amargasaurus") dinosaurs.Add("Mamenchisaurus") dinosaurs.Add("Deinonychus") dinosaurs.Add("Compsognathus") Console.WriteLine() For Each dinosaur As String In dinosaurs Console.WriteLine(dinosaur) Next Console.WriteLine(vbLf & "Capacity: {0}", dinosaurs.Capacity) Console.WriteLine("Count: {0}", dinosaurs.Count) Console.WriteLine(vbLf & "Contains(""Deinonychus""): {0}", _ dinosaurs.Contains("Deinonychus")) Console.WriteLine(vbLf & "Insert(2, ""Compsognathus"")") dinosaurs.Insert(2, "Compsognathus") Console.WriteLine() For Each dinosaur As String In dinosaurs Console.WriteLine(dinosaur) Next ' Shows how to access the list using the Item property. Console.WriteLine(vbLf & "dinosaurs(3): {0}", dinosaurs(3)) Console.WriteLine(vbLf & "Remove(""Compsognathus"")") dinosaurs.Remove("Compsognathus") Console.WriteLine() For Each dinosaur As String In dinosaurs Console.WriteLine(dinosaur) Next dinosaurs.TrimExcess() Console.WriteLine(vbLf & "TrimExcess()") Console.WriteLine("Capacity: {0}", dinosaurs.Capacity) Console.WriteLine("Count: {0}", dinosaurs.Count) dinosaurs.Clear() Console.WriteLine(vbLf & "Clear()") Console.WriteLine("Capacity: {0}", dinosaurs.Capacity) Console.WriteLine("Count: {0}", dinosaurs.Count) End SubEnd Class' 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
[<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 TyrannosaurusAmargasaurusMamenchisaurusDeinonychusCompsognathus Capacity: 8Count: 5 Contains("Deinonychus"): true Insert(2, "Compsognathus") TyrannosaurusAmargasaurusCompsognathusMamenchisaurusDeinonychusCompsognathus dinosaurs[3]: Mamenchisaurus Remove("Compsognathus") TyrannosaurusAmargasaurusMamenchisaurusDeinonychusCompsognathus TrimExcess()Capacity: 5Count: 5 Clear()Capacity: 5Count: 0 *)

Remarks

If type T implements the IEquatable<T> generic interface, the equality comparer is the Equals method of that interface; otherwise, the default equality comparer is Object.Equals.

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

Applies to

See also

  • RemoveAt(Int32)
  • RemoveRange(Int32, Int32)
  • Add(T)
  • Insert(Int32, T)
  • Performing Culture-Insensitive String Operations in Collections
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