How do I clone a generic list in C

Question

I have a generic list of objects in C   and wish to clone the list  The items within the list are cloneable  but there doesn t seem to be an option to do list Clone     Is there an easy way around this

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public static Object CloneType Object objtype        Object lstfinal   new Object         using  MemoryStream memStream   new MemoryStream                  BinaryFormatter binaryFormatter   new BinaryFormatter null  new StreamingContext StreamingContextStates Clone            binaryFormatter Serialize memStream  objtype   memStream Seek 0  SeekOrigin Begin           lstfinal   binaryFormatter Deserialize memStream              return lstfinal

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For a deep clone I use reflection as follows  public List lt T gt  CloneList lt T gt  IEnumerable lt T gt  listToClone        Type listType   listToClone GetType        Type elementType   listType GetGenericArguments   0       List lt T gt  listCopy   new List lt T gt         foreach  T item in listToClone            object itemCopy   Activator CreateInstance elementType           foreach  PropertyInfo property in elementType GetProperties                  elementType GetProperty property Name  SetValue itemCopy  property GetValue item                      listCopy Add  T itemCopy             return listCopy     You can use List or IEnumerable interchangeably

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Unless you need an actual clone of every single object inside your List lt T gt   the best way to clone a list is to create a new list with the old list as the collection parameter   List lt T gt  myList        List lt T gt  cloneOfMyList   new List lt T gt  myList     Changes to myList such as insert or remove will not affect cloneOfMyList and vice versa   The actual objects the two Lists contain are still the same however

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There is no need to flag classes as Serializable and in our tests using the Newtonsoft JsonSerializer even faster than using BinaryFormatter  With extension methods usable on every object  Standard  NET JavascriptSerializer option  public static T DeepCopy lt T gt  this T value        JavaScriptSerializer js   new JavaScriptSerializer         string json   js Serialize value        return js Deserialize lt T gt  json      Faster option using Newtonsoft JSON  public static T DeepCopy lt T gt  this T value        string json   JsonConvert SerializeObject value        return JsonConvert DeserializeObject lt T gt  json

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I ll be lucky if anybody ever reads this    but in order to not return a list of type object in my Clone methods  I created an interface   public interface IMyCloneable lt T gt        T Clone        Then I specified the extension   public static List lt T gt  Clone lt T gt  this List lt T gt  listToClone  where T   IMyCloneable lt T gt        return listToClone Select item   gt   T item Clone    ToList        And here is an implementation of the interface in my A V marking software  I wanted to have my Clone   method return a list of VidMark  while the ICloneable interface wanted my method to return a list of object    public class VidMark   IMyCloneable lt VidMark gt        public long Beg   get  set        public long End   get  set        public string Desc   get  set        public int Rank   get  set      0       public VidMark Clone                 return  VidMark this MemberwiseClone              And finally  the usage of the extension inside a class   private List lt VidMark gt   VidMarks  private List lt VidMark gt   UndoVidMarks     Other methods instantiate and fill the lists  private void SetUndoVidMarks          UndoVidMarks    VidMarks Clone        Anybody like it  Any improvements

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public static object DeepClone object obj         object objResult   null       using  var ms   new MemoryStream                  var bf   new BinaryFormatter            bf Serialize ms  obj            ms Position   0          objResult   bf Deserialize ms                return objResult     This is one way to do it with C  and  NET 2 0  Your object requires to be  Serializable     The goal is to lose all references and build new ones

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There is a simple way to clone objects in C  using a JSON serializer and deserializer   You can create an extension class   using Newtonsoft Json   static class typeExtensions        Extension        public static T jsonCloneObject lt T gt  T source            string json   JsonConvert SerializeObject source       return JsonConvert DeserializeObject lt T gt  json             To clone and object   obj clonedObj   originalObj jsonCloneObject

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public List lt TEntity gt  Clone lt TEntity gt  List lt TEntity gt  o1List  where TEntity   class   new                 List lt TEntity gt  retList   new List lt TEntity gt             try                       Type sourceType   typeof TEntity               foreach var o1 in o1List                                TEntity o2   new TEntity                    foreach  PropertyInfo propInfo in  sourceType GetProperties                                           var val   propInfo GetValue o1  null                       propInfo SetValue o2  val                                     retList Add o2                             return retList                    catch                       return retList

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public static object DeepClone object obj         object objResult   null       using  var ms   new MemoryStream                  var bf   new BinaryFormatter            bf Serialize ms  obj            ms Position   0          objResult   bf Deserialize ms                return objResult     This is one way to do it with C  and  NET 2 0  Your object requires to be  Serializable     The goal is to lose all references and build new ones

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Another thing  you could use reflection  If you ll cache this properly  then it ll clone 1 000 000 objects in 5 6 seconds  sadly  16 4 seconds with inner objects     ProtoContract ImplicitFields   ImplicitFields AllPublic   public class Person                    Job JobDescription                ProtoContract ImplicitFields   ImplicitFields AllPublic   public class Job         private static readonly Type stringType   typeof  string    public static class CopyFactory       static readonly Dictionary lt Type  PropertyInfo   gt  ProperyList   new Dictionary lt Type  PropertyInfo   gt          private static readonly MethodInfo CreateCopyReflectionMethod       static CopyFactory                 CreateCopyReflectionMethod   typeof CopyFactory  GetMethod  CreateCopyReflection   BindingFlags Static   BindingFlags Public              public static T CreateCopyReflection lt T gt  T source  where T   new                 var copyInstance   new T            var sourceType   typeof T            PropertyInfo   propList          if  ProperyList ContainsKey sourceType               propList   ProperyList sourceType           else                       propList   sourceType GetProperties BindingFlags Public   BindingFlags Instance               ProperyList Add sourceType  propList                      foreach  var prop in propList                        var value   prop GetValue source  null               prop SetValue copyInstance                  value    null  amp  amp  prop PropertyType IsClass  amp  amp  prop PropertyType    stringType   CreateCopyReflectionMethod MakeGenericMethod prop PropertyType  Invoke null  new object     value      value  null                      return copyInstance          I measured it in a simple way  by using the Watcher class    var person   new Person                   for  var i   0  i  lt  1000000  i           personList Add person       var watcher   new Stopwatch     watcher Start     var copylist   personList Select CopyFactory CreateCopyReflection  ToList     watcher Stop     var elapsed   watcher Elapsed    RESULT  With inner object PersonInstance - 16 4  PersonInstance   null - 5 6  CopyFactory is just my test class where I have dozen of tests including usage of expression  You could implement this in another form in an extension or whatever  Don t forget about caching   I didn t test serializing yet  but I doubt in an improvement with a million classes  I ll try something fast protobuf newton   P S   for the sake of reading simplicity  I only used auto-property here  I could update with FieldInfo  or you should easily implement this by your own   I recently tested the Protocol Buffers serializer with the DeepClone function out of the box  It wins with 4 2 seconds on a million simple objects  but when it comes to inner objects  it wins with the result 7 4 seconds   Serializer DeepClone personList     SUMMARY  If you don t have access to the classes  then this will help    Otherwise it depends on the count of the objects  I think you could use reflection up to 10 000 objects  maybe a bit less   but for more than this the Protocol Buffers serializer will perform better

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The following code should transfer onto a list with minimal changes    Basically it works by inserting a new random number from a greater range with each successive loop  If there exist numbers already that are the same or higher than it  shift those random numbers up one so they transfer into the new larger range of random indexes      Example Usage int   indexes   getRandomUniqueIndexArray selectFrom Length  toSet Length    for int i   0  i  lt  toSet Length  i        toSet i    selectFrom indexes i      private int   getRandomUniqueIndexArray int length  int count        if count  gt  length    count  lt  1    length  lt  1          return new int 0        int   toReturn   new int count       if count    length                for int i   0  i  lt  toReturn Length  i    toReturn i    i          return toReturn             Random r   new Random        int startPos   count - 1      for int i   startPos  i  gt   0  i--                int index   r Next length - i           for int j   startPos  j  gt  i  j--              if toReturn j   gt   index                  toReturn j             toReturn i    index             return toReturn

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There is a simple way to clone objects in C  using a JSON serializer and deserializer   You can create an extension class   using Newtonsoft Json   static class typeExtensions        Extension        public static T jsonCloneObject lt T gt  T source            string json   JsonConvert SerializeObject source       return JsonConvert DeserializeObject lt T gt  json             To clone and object   obj clonedObj   originalObj jsonCloneObject

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Using a cast may be helpful  in this case  for a shallow copy   IList CloneList IList list        IList result      result    IList Activator CreateInstance list GetType         foreach  object item in list  result Add item       return result      applied to generic list   List lt T gt  Clone lt T gt  List lt T gt  argument    gt   List lt T gt  CloneList argument

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public class CloneableList lt T gt    List lt T gt   ICloneable where T   ICloneable     public object Clone           var clone   new List lt T gt         ForEach item   gt  clone Add  T item Clone          return clone

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If you only care about value types     And you know the type   List lt int gt  newList   new List lt int gt  oldList     If you don t know the  type before  you ll need a helper function   List lt T gt  Clone lt T gt  IEnumerable lt T gt  oldList        return newList   new List lt T gt  oldList       The just   List lt string gt  myNewList   Clone myOldList

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public List lt TEntity gt  Clone lt TEntity gt  List lt TEntity gt  o1List  where TEntity   class   new                 List lt TEntity gt  retList   new List lt TEntity gt             try                       Type sourceType   typeof TEntity               foreach var o1 in o1List                                TEntity o2   new TEntity                    foreach  PropertyInfo propInfo in  sourceType GetProperties                                           var val   propInfo GetValue o1  null                       propInfo SetValue o2  val                                     retList Add o2                             return retList                    catch                       return retList

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For a shallow copy  you can instead use the GetRange method of the generic List class   List lt int gt  oldList   new List lt int gt         Populate oldList     List lt int gt  newList   oldList GetRange 0  oldList Count     Quoted from  Generics Recipes

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public static object DeepClone object obj         object objResult   null       using  var ms   new MemoryStream                  var bf   new BinaryFormatter            bf Serialize ms  obj            ms Position   0          objResult   bf Deserialize ms                return objResult     This is one way to do it with C  and  NET 2 0  Your object requires to be  Serializable     The goal is to lose all references and build new ones

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To clone a list just call  ToList    This creates a shallow copy   Microsoft  R  Roslyn C  Compiler version 2 3 2 62116 Loading context from  CSharpInteractive rsp   Type   help  for more information   gt  var x   new List lt int gt      3  4     gt  var y   x ToList     gt  x Add 5   gt  x List lt int gt  3    3  4  5    gt  y List lt int gt  2    3  4    gt

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public static object DeepClone object obj         object objResult   null       using  var ms   new MemoryStream                  var bf   new BinaryFormatter            bf Serialize ms  obj            ms Position   0          objResult   bf Deserialize ms                return objResult     This is one way to do it with C  and  NET 2 0  Your object requires to be  Serializable     The goal is to lose all references and build new ones

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You can use extension method     namespace extension       public class ext               public static List lt double gt  clone this List lt double gt  t                        List lt double gt  kop   new List lt double gt                 int x              for  x   0  x  lt  t Count  x                                  kop Add t x                              return kop                       You can clone all objects by using their value type members for example  consider this class     public class matrix       public List lt List lt double gt  gt  mat      public int rows cols      public matrix clone                     create new object         matrix copy   new matrix               firstly I can directly copy rows and cols because they are value types         copy rows   this rows            copy cols   this cols             but now I can no t directly copy mat because it is not value type so         int x             I assume I have clone method for List lt double gt          for x 0 x lt this mat count x                          copy mat Add this mat x  clone                          then mat is cloned         return copy     and copy of original is returned             Note  if you do any change on copy  or clone  it will not affect the original object

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public class CloneableList lt T gt    List lt T gt   ICloneable where T   ICloneable     public object Clone           var clone   new List lt T gt         ForEach item   gt  clone Add  T item Clone          return clone

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I ll be lucky if anybody ever reads this    but in order to not return a list of type object in my Clone methods  I created an interface   public interface IMyCloneable lt T gt        T Clone        Then I specified the extension   public static List lt T gt  Clone lt T gt  this List lt T gt  listToClone  where T   IMyCloneable lt T gt        return listToClone Select item   gt   T item Clone    ToList        And here is an implementation of the interface in my A V marking software  I wanted to have my Clone   method return a list of VidMark  while the ICloneable interface wanted my method to return a list of object    public class VidMark   IMyCloneable lt VidMark gt        public long Beg   get  set        public long End   get  set        public string Desc   get  set        public int Rank   get  set      0       public VidMark Clone                 return  VidMark this MemberwiseClone              And finally  the usage of the extension inside a class   private List lt VidMark gt   VidMarks  private List lt VidMark gt   UndoVidMarks     Other methods instantiate and fill the lists  private void SetUndoVidMarks          UndoVidMarks    VidMarks Clone        Anybody like it  Any improvements

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You can use an extension method   static class Extensions       public static IList lt T gt  Clone lt T gt  this IList lt T gt  listToClone  where T  ICloneable               return listToClone Select item   gt   T item Clone    ToList

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For a deep copy  ICloneable is the correct solution  but here s a similar approach to ICloneable using the constructor instead of the ICloneable interface   public class Student     public Student Student student          FirstName   student FirstName      LastName   student LastName         public string FirstName   get  set      public string LastName   get  set          wherever you have the list List lt Student gt  students      and then where you want to make a copy List lt Student gt  copy   students Select s   gt  new Student s   ToList      you ll need the following library where you make the copy  using System Linq   you could also use a for loop instead of System Linq  but Linq makes it concise and clean  Likewise you could do as other answers have suggested and make extension methods  etc   but none of that is necessary

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If your elements are value types  then you can just do   List lt YourType gt  newList   new List lt YourType gt  oldList     However  if they are reference types and you want a deep copy  assuming your elements properly implement ICloneable   you could do something like this   List lt ICloneable gt  oldList   new List lt ICloneable gt     List lt ICloneable gt  newList   new List lt ICloneable gt  oldList Count    oldList ForEach  item    gt                newList Add  ICloneable item Clone               Obviously  replace ICloneable in the above generics and cast with whatever your element type is that implements ICloneable   If your element type doesn t support ICloneable but does have a copy-constructor  you could do this instead   List lt YourType gt  oldList   new List lt YourType gt     List lt YourType gt  newList   new List lt YourType gt  oldList Count    oldList ForEach  item   gt                newList Add new YourType item              Personally  I would avoid ICloneable because of the need to guarantee a deep copy of all members  Instead  I d suggest the copy-constructor or a factory method like YourType CopyFrom YourType itemToCopy  that returns a new instance of YourType   Any of these options could be wrapped by a method  extension or otherwise

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You could also simply convert the list to an array using ToArray  and then clone the array using Array Clone       Depending on your needs  the methods included in the Array class could meet your needs

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For a shallow copy  you can instead use the GetRange method of the generic List class   List lt int gt  oldList   new List lt int gt         Populate oldList     List lt int gt  newList   oldList GetRange 0  oldList Count     Quoted from  Generics Recipes

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If you have already referenced Newtonsoft Json in your project and your objects are serializeable you could always use   List lt T gt  newList   JsonConvert DeserializeObject lt T gt  JsonConvert SerializeObject listToCopy     Possibly not the most efficient way to do it  but unless you re doing it 100s of 1000s of times you may not even notice the speed difference

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try this  List lt string gt  ListCopy  new List lt string gt  OldList      or try  List lt T gt  ListCopy OldList ToList

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try this  List lt string gt  ListCopy  new List lt string gt  OldList      or try  List lt T gt  ListCopy OldList ToList

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There is no need to flag classes as Serializable and in our tests using the Newtonsoft JsonSerializer even faster than using BinaryFormatter  With extension methods usable on every object  Standard  NET JavascriptSerializer option  public static T DeepCopy lt T gt  this T value        JavaScriptSerializer js   new JavaScriptSerializer         string json   js Serialize value        return js Deserialize lt T gt  json      Faster option using Newtonsoft JSON  public static T DeepCopy lt T gt  this T value        string json   JsonConvert SerializeObject value        return JsonConvert DeserializeObject lt T gt  json

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Use AutoMapper  or whatever mapping lib you prefer  to clone is simple and a lot maintainable   Define your mapping   Mapper CreateMap lt YourType  YourType gt       Do the magic   YourTypeList ConvertAll Mapper Map lt YourType  YourType gt

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For a shallow copy  you can instead use the GetRange method of the generic List class   List lt int gt  oldList   new List lt int gt         Populate oldList     List lt int gt  newList   oldList GetRange 0  oldList Count     Quoted from  Generics Recipes

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If you need a cloned list with the same capacity  you can try this   public static List lt T gt  Clone lt T gt  this List lt T gt  oldList        var newList   new List lt T gt  oldList Capacity       newList AddRange oldList       return newList

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For a deep clone I use reflection as follows  public List lt T gt  CloneList lt T gt  IEnumerable lt T gt  listToClone        Type listType   listToClone GetType        Type elementType   listType GetGenericArguments   0       List lt T gt  listCopy   new List lt T gt         foreach  T item in listToClone            object itemCopy   Activator CreateInstance elementType           foreach  PropertyInfo property in elementType GetProperties                  elementType GetProperty property Name  SetValue itemCopy  property GetValue item                      listCopy Add  T itemCopy             return listCopy     You can use List or IEnumerable interchangeably

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After a slight modification you can also clone   public static T DeepClone lt T gt  T obj        T objResult      using  MemoryStream ms   new MemoryStream                  BinaryFormatter bf   new BinaryFormatter            bf Serialize ms  obj           ms Position   0          objResult    T bf Deserialize ms             return objResult

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I ve made for my own some extension which converts ICollection of items that not implement IClonable  static class CollectionExtensions       public static ICollection lt T gt  Clone lt T gt  this ICollection lt T gt  listToClone                var array   new T listToClone Count           listToClone CopyTo array 0           return array ToList

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The following code should transfer onto a list with minimal changes    Basically it works by inserting a new random number from a greater range with each successive loop  If there exist numbers already that are the same or higher than it  shift those random numbers up one so they transfer into the new larger range of random indexes      Example Usage int   indexes   getRandomUniqueIndexArray selectFrom Length  toSet Length    for int i   0  i  lt  toSet Length  i        toSet i    selectFrom indexes i      private int   getRandomUniqueIndexArray int length  int count        if count  gt  length    count  lt  1    length  lt  1          return new int 0        int   toReturn   new int count       if count    length                for int i   0  i  lt  toReturn Length  i    toReturn i    i          return toReturn             Random r   new Random        int startPos   count - 1      for int i   startPos  i  gt   0  i--                int index   r Next length - i           for int j   startPos  j  gt  i  j--              if toReturn j   gt   index                  toReturn j             toReturn i    index             return toReturn

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I use automapper to copy an object  I just setup a mapping that maps one object to itself  You can wrap this operation any way you like    http   automapper codeplex com

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If you only care about value types     And you know the type   List lt int gt  newList   new List lt int gt  oldList     If you don t know the  type before  you ll need a helper function   List lt T gt  Clone lt T gt  IEnumerable lt T gt  oldList        return newList   new List lt T gt  oldList       The just   List lt string gt  myNewList   Clone myOldList

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You can use an extension method   static class Extensions       public static IList lt T gt  Clone lt T gt  this IList lt T gt  listToClone  where T  ICloneable               return listToClone Select item   gt   T item Clone    ToList

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Another thing  you could use reflection  If you ll cache this properly  then it ll clone 1 000 000 objects in 5 6 seconds  sadly  16 4 seconds with inner objects     ProtoContract ImplicitFields   ImplicitFields AllPublic   public class Person                    Job JobDescription                ProtoContract ImplicitFields   ImplicitFields AllPublic   public class Job         private static readonly Type stringType   typeof  string    public static class CopyFactory       static readonly Dictionary lt Type  PropertyInfo   gt  ProperyList   new Dictionary lt Type  PropertyInfo   gt          private static readonly MethodInfo CreateCopyReflectionMethod       static CopyFactory                 CreateCopyReflectionMethod   typeof CopyFactory  GetMethod  CreateCopyReflection   BindingFlags Static   BindingFlags Public              public static T CreateCopyReflection lt T gt  T source  where T   new                 var copyInstance   new T            var sourceType   typeof T            PropertyInfo   propList          if  ProperyList ContainsKey sourceType               propList   ProperyList sourceType           else                       propList   sourceType GetProperties BindingFlags Public   BindingFlags Instance               ProperyList Add sourceType  propList                      foreach  var prop in propList                        var value   prop GetValue source  null               prop SetValue copyInstance                  value    null  amp  amp  prop PropertyType IsClass  amp  amp  prop PropertyType    stringType   CreateCopyReflectionMethod MakeGenericMethod prop PropertyType  Invoke null  new object     value      value  null                      return copyInstance          I measured it in a simple way  by using the Watcher class    var person   new Person                   for  var i   0  i  lt  1000000  i           personList Add person       var watcher   new Stopwatch     watcher Start     var copylist   personList Select CopyFactory CreateCopyReflection  ToList     watcher Stop     var elapsed   watcher Elapsed    RESULT  With inner object PersonInstance - 16 4  PersonInstance   null - 5 6  CopyFactory is just my test class where I have dozen of tests including usage of expression  You could implement this in another form in an extension or whatever  Don t forget about caching   I didn t test serializing yet  but I doubt in an improvement with a million classes  I ll try something fast protobuf newton   P S   for the sake of reading simplicity  I only used auto-property here  I could update with FieldInfo  or you should easily implement this by your own   I recently tested the Protocol Buffers serializer with the DeepClone function out of the box  It wins with 4 2 seconds on a million simple objects  but when it comes to inner objects  it wins with the result 7 4 seconds   Serializer DeepClone personList     SUMMARY  If you don t have access to the classes  then this will help    Otherwise it depends on the count of the objects  I think you could use reflection up to 10 000 objects  maybe a bit less   but for more than this the Protocol Buffers serializer will perform better

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If you need a cloned list with the same capacity  you can try this   public static List lt T gt  Clone lt T gt  this List lt T gt  oldList        var newList   new List lt T gt  oldList Capacity       newList AddRange oldList       return newList

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For a shallow copy  you can instead use the GetRange method of the generic List class   List lt int gt  oldList   new List lt int gt         Populate oldList     List lt int gt  newList   oldList GetRange 0  oldList Count     Quoted from  Generics Recipes

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You can use an extension method   static class Extensions       public static IList lt T gt  Clone lt T gt  this IList lt T gt  listToClone  where T  ICloneable               return listToClone Select item   gt   T item Clone    ToList

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I use automapper to copy an object  I just setup a mapping that maps one object to itself  You can wrap this operation any way you like    http   automapper codeplex com

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You could also simply convert the list to an array using ToArray  and then clone the array using Array Clone       Depending on your needs  the methods included in the Array class could meet your needs

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Unless you need an actual clone of every single object inside your List lt T gt   the best way to clone a list is to create a new list with the old list as the collection parameter   List lt T gt  myList        List lt T gt  cloneOfMyList   new List lt T gt  myList     Changes to myList such as insert or remove will not affect cloneOfMyList and vice versa   The actual objects the two Lists contain are still the same however

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If your elements are value types  then you can just do   List lt YourType gt  newList   new List lt YourType gt  oldList     However  if they are reference types and you want a deep copy  assuming your elements properly implement ICloneable   you could do something like this   List lt ICloneable gt  oldList   new List lt ICloneable gt     List lt ICloneable gt  newList   new List lt ICloneable gt  oldList Count    oldList ForEach  item    gt                newList Add  ICloneable item Clone               Obviously  replace ICloneable in the above generics and cast with whatever your element type is that implements ICloneable   If your element type doesn t support ICloneable but does have a copy-constructor  you could do this instead   List lt YourType gt  oldList   new List lt YourType gt     List lt YourType gt  newList   new List lt YourType gt  oldList Count    oldList ForEach  item   gt                newList Add new YourType item              Personally  I would avoid ICloneable because of the need to guarantee a deep copy of all members  Instead  I d suggest the copy-constructor or a factory method like YourType CopyFrom YourType itemToCopy  that returns a new instance of YourType   Any of these options could be wrapped by a method  extension or otherwise

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Use AutoMapper  or whatever mapping lib you prefer  to clone is simple and a lot maintainable   Define your mapping   Mapper CreateMap lt YourType  YourType gt       Do the magic   YourTypeList ConvertAll Mapper Map lt YourType  YourType gt

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For a deep copy  ICloneable is the correct solution  but here s a similar approach to ICloneable using the constructor instead of the ICloneable interface   public class Student     public Student Student student          FirstName   student FirstName      LastName   student LastName         public string FirstName   get  set      public string LastName   get  set          wherever you have the list List lt Student gt  students      and then where you want to make a copy List lt Student gt  copy   students Select s   gt  new Student s   ToList      you ll need the following library where you make the copy  using System Linq   you could also use a for loop instead of System Linq  but Linq makes it concise and clean  Likewise you could do as other answers have suggested and make extension methods  etc   but none of that is necessary

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I ve made for my own some extension which converts ICollection of items that not implement IClonable  static class CollectionExtensions       public static ICollection lt T gt  Clone lt T gt  this ICollection lt T gt  listToClone                var array   new T listToClone Count           listToClone CopyTo array 0           return array ToList

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If your elements are value types  then you can just do   List lt YourType gt  newList   new List lt YourType gt  oldList     However  if they are reference types and you want a deep copy  assuming your elements properly implement ICloneable   you could do something like this   List lt ICloneable gt  oldList   new List lt ICloneable gt     List lt ICloneable gt  newList   new List lt ICloneable gt  oldList Count    oldList ForEach  item    gt                newList Add  ICloneable item Clone               Obviously  replace ICloneable in the above generics and cast with whatever your element type is that implements ICloneable   If your element type doesn t support ICloneable but does have a copy-constructor  you could do this instead   List lt YourType gt  oldList   new List lt YourType gt     List lt YourType gt  newList   new List lt YourType gt  oldList Count    oldList ForEach  item   gt                newList Add new YourType item              Personally  I would avoid ICloneable because of the need to guarantee a deep copy of all members  Instead  I d suggest the copy-constructor or a factory method like YourType CopyFrom YourType itemToCopy  that returns a new instance of YourType   Any of these options could be wrapped by a method  extension or otherwise

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You can use extension method     namespace extension       public class ext               public static List lt double gt  clone this List lt double gt  t                        List lt double gt  kop   new List lt double gt                 int x              for  x   0  x  lt  t Count  x                                  kop Add t x                              return kop                       You can clone all objects by using their value type members for example  consider this class     public class matrix       public List lt List lt double gt  gt  mat      public int rows cols      public matrix clone                     create new object         matrix copy   new matrix               firstly I can directly copy rows and cols because they are value types         copy rows   this rows            copy cols   this cols             but now I can no t directly copy mat because it is not value type so         int x             I assume I have clone method for List lt double gt          for x 0 x lt this mat count x                          copy mat Add this mat x  clone                          then mat is cloned         return copy     and copy of original is returned             Note  if you do any change on copy  or clone  it will not affect the original object

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If you only care about value types     And you know the type   List lt int gt  newList   new List lt int gt  oldList     If you don t know the  type before  you ll need a helper function   List lt T gt  Clone lt T gt  IEnumerable lt T gt  oldList        return newList   new List lt T gt  oldList       The just   List lt string gt  myNewList   Clone myOldList

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You can use an extension method   static class Extensions       public static IList lt T gt  Clone lt T gt  this IList lt T gt  listToClone  where T  ICloneable               return listToClone Select item   gt   T item Clone    ToList

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If you only care about value types     And you know the type   List lt int gt  newList   new List lt int gt  oldList     If you don t know the  type before  you ll need a helper function   List lt T gt  Clone lt T gt  IEnumerable lt T gt  oldList        return newList   new List lt T gt  oldList       The just   List lt string gt  myNewList   Clone myOldList

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After a slight modification you can also clone   public static T DeepClone lt T gt  T obj        T objResult      using  MemoryStream ms   new MemoryStream                  BinaryFormatter bf   new BinaryFormatter            bf Serialize ms  obj           ms Position   0          objResult    T bf Deserialize ms             return objResult

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To clone a list just call  ToList    This creates a shallow copy   Microsoft  R  Roslyn C  Compiler version 2 3 2 62116 Loading context from  CSharpInteractive rsp   Type   help  for more information   gt  var x   new List lt int gt      3  4     gt  var y   x ToList     gt  x Add 5   gt  x List lt int gt  3    3  4  5    gt  y List lt int gt  2    3  4    gt

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Using a cast may be helpful  in this case  for a shallow copy   IList CloneList IList list        IList result      result    IList Activator CreateInstance list GetType         foreach  object item in list  result Add item       return result      applied to generic list   List lt T gt  Clone lt T gt  List lt T gt  argument    gt   List lt T gt  CloneList argument

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If your elements are value types  then you can just do   List lt YourType gt  newList   new List lt YourType gt  oldList     However  if they are reference types and you want a deep copy  assuming your elements properly implement ICloneable   you could do something like this   List lt ICloneable gt  oldList   new List lt ICloneable gt     List lt ICloneable gt  newList   new List lt ICloneable gt  oldList Count    oldList ForEach  item    gt                newList Add  ICloneable item Clone               Obviously  replace ICloneable in the above generics and cast with whatever your element type is that implements ICloneable   If your element type doesn t support ICloneable but does have a copy-constructor  you could do this instead   List lt YourType gt  oldList   new List lt YourType gt     List lt YourType gt  newList   new List lt YourType gt  oldList Count    oldList ForEach  item   gt                newList Add new YourType item              Personally  I would avoid ICloneable because of the need to guarantee a deep copy of all members  Instead  I d suggest the copy-constructor or a factory method like YourType CopyFrom YourType itemToCopy  that returns a new instance of YourType   Any of these options could be wrapped by a method  extension or otherwise

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If you have already referenced Newtonsoft Json in your project and your objects are serializeable you could always use   List lt T gt  newList   JsonConvert DeserializeObject lt T gt  JsonConvert SerializeObject listToCopy     Possibly not the most efficient way to do it  but unless you re doing it 100s of 1000s of times you may not even notice the speed difference

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public static Object CloneType Object objtype        Object lstfinal   new Object         using  MemoryStream memStream   new MemoryStream                  BinaryFormatter binaryFormatter   new BinaryFormatter null  new StreamingContext StreamingContextStates Clone            binaryFormatter Serialize memStream  objtype   memStream Seek 0  SeekOrigin Begin           lstfinal   binaryFormatter Deserialize memStream              return lstfinal

[c#] How do I clone a generic list in C#?

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