Как скопировать arraylist java
Чтобы скопировать ArrayList , можно использовать метод clone() , который создаст копию списка. Также можно создать новый объект ArrayList и использовать метод addAll() для добавления всех элементов из исходного списка в новый список.
ArrayListString> originalList = new ArrayList<>(); // добавляем элементы в оригинальный список originalList.add("один"); originalList.add("два"); originalList.add("три"); // создаем новый список и добавляем все элементы из оригинального списка ArrayListString> copiedList = new ArrayList<>(); copiedList.addAll(originalList); // проверяем, что списки одинаковые System.out.println(originalList.equals(copiedList)); // => true Также можно использовать конструктор ArrayList(Collection c) , который создает новый список на основе коллекции. Например:
ArrayListString> originalList = new ArrayList<>(); // добавляем элементы в оригинальный список originalList.add("один"); originalList.add("два"); originalList.add("три"); // создаем новый список на основе оригинального ArrayListString> copiedList = new ArrayList<>(originalList); // проверяем, что списки одинаковые System.out.println(originalList.equals(copiedList)); // => true Как создать копию List?
Но потом я понял, что List — это ссылочный тип. Поэтому присвоение одного объекта другому, это просто копирование указателя.
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задан 14 окт 2019 в 16:29
Dmitry Machikhelyan Dmitry Machikhelyan
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Конструктор List принимает IEnumerable
14 окт 2019 в 16:33
@EvgeniyZ, а почему бы не Clone ? Но в обоих случаях элементы списка тоже ссылочные, а по вопросу непонятно\, что с ними требуется сделать.
14 окт 2019 в 16:43
List полностью скопировать, его элементы тоже должны быть скопированы.
14 окт 2019 в 16:52
2 ответа 2
Сортировка: Сброс на вариант по умолчанию
Для клонирования того же класса в C# предусмотрен интерфейс ICloneable. Реализовав его, вы сможете вызвать метод Clone() , который отдаст вам копию объекта.
Реализация такого класса будет выглядеть примерно так:
class Test : ICloneable < public string Name < get; set; >public int Value < get; set; >public object Clone() => MemberwiseClone(); > Заметьте, тут я использовал MemberwiseClone() , он сам сделает копию текущего объекта, но не глубокую! Это надо учесть.
Дальше нам остается создать новую коллекцию и перенести в нее копии объектов, что то вроде этого:
foreach(var item in mainList)
Для облегчения этого процесса можно сделать например расширение, которое при помощи того же LINQ в пару строк реализует нам все необходимое:
static class Extensions < public static IListClone(this IList source) where T : ICloneable => source.Select(item => (T)item.Clone()).ToList(); > var copiedList = mainList.Clone(); Небольшой тест этого всего:
var mainList = new List < new Test < Name = "Test", Value = 111 >>; var copiedList = mainList.Clone(); mainList[0].Value = 1; copiedList[0].Value = 2; Console.WriteLine(mainList[0].Value); Console.WriteLine(copiedList[0].Value); Результатом будет два числа (1 и 2).
List.Add(T) Метод
Некоторые сведения относятся к предварительной версии продукта, в которую до выпуска могут быть внесены существенные изменения. Майкрософт не предоставляет никаких гарантий, явных или подразумеваемых, относительно приведенных здесь сведений.
Добавляет объект в конец коллекции List .
public: virtual void Add(T item);public void Add (T item);abstract member Add : 'T -> unit override this.Add : 'T -> unitPublic Sub Add (item As T)Параметры
Реализации
Примеры
В следующем примере показано, как добавить, удалить и вставить простой бизнес-объект в 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. Listparts = 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\"): ", 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]: ", 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""): ", 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]: ", 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 by its type // abbreviation ResizeArray to avoid conflicts with the F# List module. // Note: In F# code, F# linked lists are usually preferred over // ResizeArray when an extendable collection is required. let parts = ResizeArray() parts.Add() parts.Add() parts.Add() parts.Add() parts.Add() parts.Add() // 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()) // 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() |> 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
В следующем примере демонстрируется несколько свойств и методов универсального List класса, включая Add метод . Конструктор без параметров используется для создания списка строк с емкостью 0. Отображается Capacity свойство , а затем Add метод используется для добавления нескольких элементов. Элементы перечислены, и Capacity свойство отображается снова вместе со свойством Count , чтобы показать, что емкость была увеличена по мере необходимости.
Другие свойства и методы используются для поиска, вставки и удаления элементов из списка и, наконец, для очистки списка.
using namespace System; using namespace System::Collections::Generic; void main() < List^ dinosaurs = gcnew List(); Console::WriteLine("\nCapacity: ", 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: ", dinosaurs->Capacity); Console::WriteLine("Count: ", dinosaurs->Count); Console::WriteLine("\nContains(\"Deinonychus\"): ", 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]: ", 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: ", dinosaurs->Capacity); Console::WriteLine("Count: ", dinosaurs->Count); dinosaurs->Clear(); Console::WriteLine("\nClear()"); Console::WriteLine("Capacity: ", dinosaurs->Capacity); Console::WriteLine("Count: ", 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 */ List dinosaurs = new List(); Console.WriteLine("\nCapacity: ", 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: ", dinosaurs.Capacity); Console.WriteLine("Count: ", dinosaurs.Count); Console.WriteLine("\nContains(\"Deinonychus\"): ", 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]: ", 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: ", dinosaurs.Capacity); Console.WriteLine("Count: ", dinosaurs.Count); dinosaurs.Clear(); Console.WriteLine("\nClear()"); Console.WriteLine("Capacity: ", dinosaurs.Capacity); Console.WriteLine("Count: ", 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 Public Class Example Public Shared Sub Main() Dim dinosaurs As New List(Of String) Console.WriteLine(vbLf & "Capacity: ", 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: ", dinosaurs.Capacity) Console.WriteLine("Count: ", dinosaurs.Count) Console.WriteLine(vbLf & "Contains(""Deinonychus""): ", _ 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): ", 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: ", dinosaurs.Capacity) Console.WriteLine("Count: ", dinosaurs.Count) dinosaurs.Clear() Console.WriteLine(vbLf & "Clear()") Console.WriteLine("Capacity: ", dinosaurs.Capacity) Console.WriteLine("Count: ", dinosaurs.Count) End Sub End 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 [] let main argv = // We refer to System.Collections.Generic.List by its type // abbreviation ResizeArray to avoid conflict with the List module. // Note: In F# code, F# linked lists are usually preferred over // 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 *)
Комментарии
Если Count меньше Capacity, этот метод является операцией O(1). Если емкость необходимо увеличить для размещения нового элемента, этот метод становится операцией O(n), где n — .Count
How do I copy items from list to list without foreach?
or if you’re using C# 3 and .NET 3.5, with Linq, you can do this:
List copy = original.ToList(); I see that this answer is still getting upvotes. Well, here’s a secret for ya: the above answer is still using a foreach. Please don’t upvote this any further.
community wiki
If the items are of type MyClass instead of Integer , does it copy the items too, or just reference them?
Jun 6, 2014 at 14:14
Not working with Non-primitive types. List
Apr 3, 2015 at 10:59
It works with all types, as long as lstStudentClass is an IEnumerable
Apr 3, 2015 at 11:05
what is the meaning of (original); at the end
Sep 13, 2015 at 14:40
@PedroMoreira For complex object you can do: origninal.Select(o => new Complex(o)).ToList() to get a list of new objects, not copied references
Jun 20, 2017 at 16:25
To add the contents of one list to another list which already exists, you can use:
targetList.AddRange(sourceList); If you’re just wanting to create a new copy of the list, see the top answer.
user14955720
answered Dec 23, 2009 at 11:20
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@mrmillsy: Well they do different things. My answer is focused on «I already have a list, and I want to copy things to it»
Mar 1, 2013 at 12:44
True. My question would probably be better suited to a new question anyway. Thanks for the reply though.
Mar 1, 2013 at 12:47
If you wanted to replace the contents of an existing list completely, you would call targetList.Clear() first.
Jul 20, 2013 at 15:16
This is the correct answer as copying implies adding, not replacing. The OP asked for copying ITEMS not the entire collection.
Jan 16, 2021 at 3:22
For a list of elements
List lstTest = new List(); lstTest.Add("test1"); lstTest.Add("test2"); lstTest.Add("test3"); lstTest.Add("test4"); lstTest.Add("test5"); lstTest.Add("test6"); If you want to copy all the elements
List lstNew = new List(); lstNew.AddRange(lstTest); If you want to copy the first 3 elements
List lstNew = lstTest.GetRange(0, 3); 850 1 1 gold badge 13 13 silver badges 36 36 bronze badges
answered May 10, 2012 at 9:47
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This is the correct answer. AddRange does not specify it in the docs, that it copies or just adds objects by reference, but if you search the implementation, it uses Array.Copy (static) to copy the data.
Apr 26, 2021 at 19:43
And this is if copying a single property to another list is needed:
targetList.AddRange(sourceList.Select(i => i.NeededProperty)); answered Aug 24, 2016 at 20:02
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This method will create a copy of your list but your type should be serializable.
Use:
List lstStudent = db.Students.Where(s => s.DOB < DateTime.Now).ToList().CopyList(); Method:
public static List CopyList(this List lst) < ListlstCopy = new List(); foreach (var item in lst) < using (MemoryStream stream = new MemoryStream()) < BinaryFormatter formatter = new BinaryFormatter(); formatter.Serialize(stream, item); stream.Position = 0; lstCopy.Add((T)formatter.Deserialize(stream)); >> return lstCopy; > answered Apr 3, 2015 at 11:15
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Does the serialization create a significant performance penalty?
Nov 2, 2016 at 13:43
Easy to map different set of list by linq without for loop
var List1= new List(); var List2= new List(); var List2 = List1.Select(p => new Entities2 < EntityCode = p.EntityCode, EntityId = p.EntityId, EntityName = p.EntityName >).ToList(); answered Mar 25, 2020 at 10:50
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Adding to the top answers, if you want copies of "the objects in the list", then you can use Select and make the copies. (While the other answers make "a copy of a list", this answer makes "a list of copies").
Suppose your item has a Copy method:
List newList = oldList.Select(item => item.Copy()).ToList(); Or that you can create a new object from the previous one with a constructor:
List newList = oldList.Select(item => new MyObject(item)).ToList(); The result of Select is an IEnumerable that you can also pass to AddRange for instance, if your goal is to add to an existing list.