List.Remove[T] Method
Definition Namespace: System.Collections.Generic Assembly:System.Collections.dll Assembly:mscorlib.dll Assembly:netstandard.dll
Important
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In this article
Removes the first occurrence of a specific object from the List. 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. 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.
Implements Remove[T]
Examples
The following example demonstrates how to add, remove, and insert a simple business object in a List.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 { 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 parts = new List[]; // 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. [] 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 [] let main argv = // We refer to System.Collections.Generic.List to avoid conflicts with the F# List module. // Note: In F# code, F# linked lists are usually preferred over // ResizeArray by its type // abbreviation ResizeArray 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
If type T implements the IEquatable 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