How do I clone a range of array elements to a new array

Question

I have an array X of 10 elements  I would like to create a new array containing all the elements from X that begin at index 3 and ends in index 7  Sure I can easily write a loop that will do it for me but I would like to keep my code as clean as possible  Is there a method in C  that can do it for me   Something like  pseudo code    Array NewArray   oldArray createNewArrayFromRange int BeginIndex   int EndIndex    Array Copy doesn t fit my needs  I need the items in the new array to be clones  Array copy is just a C-Style memcpy equivalent  it s not what I m looking for

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How about useing Array ConstrainedCopy   int   ArrayOne   new int 8   1 2 3 4 5 6 7 8   int   ArrayTwo   new int 5   Array ConstrainedCopy ArrayOne  3  ArrayTwo  0  7-3       Below is my original post   It will not work  You could use Array CopyTo   int   ArrayOne   new int 8   1 2 3 4 5 6 7 8   int   ArrayTwo   new int 5   ArrayOne CopyTo ArrayTwo 3     starts copy at index 3 until it reaches end of                                either array

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Code from the System Private CoreLib dll    public static T   GetSubArray lt T gt  T   array  Range range        if  array    null                ThrowHelper ThrowArgumentNullException ExceptionArgument array              int Offset  int Length  offsetAndLength   range GetOffsetAndLength array Length       int item   offsetAndLength Offset      int item2   offsetAndLength Length      if  default T     null    typeof T       array GetType                  if  item2    0                        return Array Empty lt T gt                       T   array2   new T item2           Buffer Memmove ref Unsafe As lt byte  T gt  ref array2 GetRawSzArrayData     ref Unsafe Add ref Unsafe As lt byte  T gt  ref array GetRawSzArrayData     item    uint item2           return array2            T   array3    T   Array CreateInstance array GetType   GetElementType    item2       Array Copy array  item  array3  0  item2       return array3

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This is the optimal way  I found  to do this   private void GetSubArrayThroughArraySegment       int   array     10  20  30      ArraySegment lt int gt  segment   new ArraySegment lt int gt  array   1  2     Console WriteLine  -- Array --      int   original   segment Array    foreach  int value in original          Console WriteLine value         Console WriteLine  -- Offset --      Console WriteLine segment Offset     Console WriteLine  -- Count --      Console WriteLine segment Count      Console WriteLine  -- Range --      for  int i   segment Offset  i  lt   segment Count  i            Console WriteLine segment Array i            Hope It Helps

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In C  8  they ve introduced a new Range and Index type  which can be used like this  int   a     0  1  2  3  4  5  6  7  8  9    Index i1   3      number 3 from beginning Index i2    4     number 4 from end var slice   a i1  i2        3  4  5    References   https   docs microsoft com en-us dotnet core whats-new dotnet-core-3-0 ranges-and-indices https   devblogs microsoft com dotnet building-c-8-0

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You can use Array Copy      to copy into the new array after you ve created it  but I don t think there s a method which creates the new array and copies a range of elements   If you re using  NET 3 5 you could use LINQ   var newArray   array Skip 3  Take 5  ToArray      but that will be somewhat less efficient   See this answer to a similar question for options for more specific situations

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I m not sure how deep it really is  but   MyArray ToList lt TSource gt    GetRange beginningIndex  endIndex  ToArray    It s a bit of overhead  but it might cut out an unnecessary method

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Cloning elements in an array is not something that can be done in a universal way  Do you want deep cloning or a simple copy of all members   Let s go for the  best effort  approach  cloning objects using the ICloneable interface or binary serialization   public static class ArrayExtensions     public static T   SubArray lt T gt  this T   array  int index  int length          T   result   new T length        for  int i index i lt length index  amp  amp  i lt array Length i                 if  array i  is ICloneable            result i-index     T    ICloneable array i   Clone           else           result i-index     T  CloneObject array i               return result         private static object CloneObject object obj          BinaryFormatter formatter   new BinaryFormatter         using  MemoryStream stream   new MemoryStream                formatter Serialize stream  obj          stream Seek 0 SeekOrigin Begin          return formatter Deserialize stream                 This is not a perfect solution  because there simply is none that will work for any type of object

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Have you considered using ArraySegment    http   msdn microsoft com en-us library 1hsbd92d aspx

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I see you want to do Cloning  not just copying references  In this case you can use  Select to project array members to their clones  For example  if your elements implemented IClonable you could do something like this   var newArray   array Skip 3  Take 5  Select eachElement   gt  eachElement Clone    ToArray      Note  This solution requires  NET Framework 3 5

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It does not meet your cloning requirement  but it seems simpler than many answers to do   Array NewArray   new ArraySegment oldArray BeginIndex   int Count  ToArray

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You can take class made by Microsoft   internal class Set lt TElement gt        private int    buckets      private Slot    slots      private int  count      private int  freeList      private readonly IEqualityComparer lt TElement gt   comparer       public Set             this null                   public Set IEqualityComparer lt TElement gt  comparer                if  comparer    null              comparer   EqualityComparer lt TElement gt  Default           comparer   comparer           buckets   new int 7            slots   new Slot 7            freeList   -1             public bool Add TElement value                return  Find value  true              public bool Contains TElement value                return Find value  false              public bool Remove TElement value                var hashCode   InternalGetHashCode value           var index1   hashCode    buckets Length          var index2   -1          for  var index3    buckets index1  - 1  index3  gt   0  index3    slots index3  Next                        if   slots index3  HashCode    hashCode  amp  amp   comparer Equals  slots index3  Value  value                                 if  index2  lt  0                       buckets index1     slots index3  Next   1                  else                      slots index2  Next    slots index3  Next                   slots index3  HashCode   -1                   slots index3  Value   default TElement                    slots index3  Next    freeList                   freeList   index3                  return true                            index2   index3                    return false             private bool Find TElement value  bool add                var hashCode   InternalGetHashCode value           for  var index    buckets hashCode    buckets Length  - 1  index  gt   0  index    slots index  Next                        if   slots index  HashCode    hashCode  amp  amp   comparer Equals  slots index  Value  value                   return true                    if  add                        int index1              if   freeList  gt   0                                index1    freeList                   freeList    slots index1  Next                            else                               if   count     slots Length                      Resize                    index1    count                     count                            int index2   hashCode    buckets Length               slots index1  HashCode   hashCode               slots index1  Value   value               slots index1  Next    buckets index2  - 1               buckets index2    index1   1                    return false             private void Resize                 var length   checked  count   2   1           var numArray   new int length           var slotArray   new Slot length           Array Copy  slots  0  slotArray  0   count           for  var index1   0  index1  lt   count    index1                        int index2   slotArray index1  HashCode   length              slotArray index1  Next   numArray index2  - 1              numArray index2    index1   1                     buckets   numArray           slots   slotArray             internal int InternalGetHashCode TElement value                if  value    null              return  comparer GetHashCode value   amp  int MaxValue          return 0             internal struct Slot               internal int HashCode          internal TElement Value          internal int Next            and then   public static T   GetSub lt T gt  this T   first  T   second                var items   IntersectIteratorWithIndex first  second           if   items Any    return new T                  var index   items First   Item2          var length   first Count   - index          var subArray   new T length           Array Copy first  index  subArray  0  length           return subArray             private static IEnumerable lt Tuple lt T  Int32 gt  gt  IntersectIteratorWithIndex lt T gt  IEnumerable lt T gt  first  IEnumerable lt T gt  second                var firstList   first ToList            var set   new Set lt T gt             foreach  var i in second              set Add i           foreach  var i in firstList                        if  set Remove i                   yield return new Tuple lt T  Int32 gt  i  firstList IndexOf i

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I think that the code you are looking for is   Array Copy oldArray  0  newArray  BeginIndex  EndIndex - BeginIndex

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use extention method    public static T   Slice lt T gt  this T   source  int start  int end                   Handles negative ends          if  end  lt  0                        end   source Length   end                    int len   end - start              Return new array          T   res   new T len           for  int i   0  i  lt  len  i                          res i    source i   start                     return res          and you can use it   var NewArray   OldArray Slice 3 7

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Array ConstrainedCopy will work   public static void ConstrainedCopy       Array sourceArray      int sourceIndex      Array destinationArray      int destinationIndex      int length

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How about this   public T   CloneCopy T   array  int startIndex  int endIndex  where T   ICloneable       T   retArray   new T endIndex - startIndex       for  int i   startIndex  i  lt  endIndex  i                  array i - startIndex    array i  Clone              return retArray       You then need to implement the ICloneable interface on all of the classes you need to use this on but that should do it

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You can do this fairly easially                    object   foo   new object 10       object   bar   new object 7          Array Copy foo  3  bar  0  7

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As an alternative to copying the data you can make a wrapper that gives you access to a part of the original array as if it was a copy of the part of the array  The advantage is that you don t get another copy of the data in memory  and the drawback is a slight overhead when accessing the data   public class SubArray lt T gt    IEnumerable lt T gt        private T    original     private int  start      public SubArray T   original  int start  int len           original   original         start   start        Length   len           public T this int index          get            if  index  lt  0    index  gt   Length  throw new IndexOutOfRangeException             return  original  start   index                    public int Length   get  private set        public IEnumerator lt T gt  GetEnumerator           for  int i   0  i  lt  Length  i              yield return  original  start   i                    IEnumerator IEnumerable GetEnumerator           return GetEnumerator              Usage   int   original     1  2  3  4  5    SubArray lt int gt  copy   new SubArray lt int gt  original  2  2    Console WriteLine copy Length      shows  2 Console WriteLine copy 0       shows  3 foreach  int i in copy  Console WriteLine i      shows 3 and 4

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Building on Marc s answer but adding the desired cloning behaviour public static T   CloneSubArray lt T gt  this T   data  int index  int length      where T   ICloneable       T   result   new T length       for  int i   0  i  lt  length  i                   var original   data index   i           if  original    null              result i     T original Clone                    return result     And if implementing ICloneable is too much like hard work a reflective one using H  vard Stranden   s Copyable library to do the heavy lifting required  using OX Copyable   public static T   DeepCopySubArray lt T gt       this T   data  int index  int length        T   result   new T length       for  int i   0  i  lt  length  i                   var original   data index   i           if  original    null              result i     T original Copy                    return result     Note that the OX Copyable implementation works with any of   For the automated copy to work  though  one of the following statements must hold for instance   Its type must have a parameterless constructor  or It must be a Copyable  or It must have an IInstanceProvider registered for its type    So this should cover almost any situation you have  If you are cloning objects where the sub graph contains things like db connections or file stream handles you obviously have issues but that it true for any generalized deep copy  If you want to use some other deep copy approach instead this article lists several others so I would suggest not trying to write your own

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The following code does it in one line      Source array string   Source   new string      A    B    C    D        Extracting a slice into another array string   Slice   new List lt string gt  Source  GetRange 2  2  ToArray

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You could add it as an extension method   public static T   SubArray lt T gt  this T   data  int index  int length        T   result   new T length       Array Copy data  index  result  0  length       return result    static void Main         int   data     0  1  2  3  4  5  6  7  8  9        int   sub   data SubArray 3  4      contains  3 4 5 6        Update re cloning  which wasn t obvious in the original question   If you really want a deep clone  something like   public static T   SubArrayDeepClone lt T gt  this T   data  int index  int length        T   arrCopy   new T length       Array Copy data  index  arrCopy  0  length       using  MemoryStream ms   new MemoryStream                  var bf   new BinaryFormatter            bf Serialize ms  arrCopy           ms Position   0          return  T   bf Deserialize ms             This does require the objects to be serializable   Serializable  or ISerializable   though  You could easily substitute for any other serializer as appropriate - XmlSerializer  DataContractSerializer  protobuf-net  etc   Note that deep clone is tricky without serialization  in particular  ICloneable is hard to trust in most cases

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In C  8 0  you can now do many fancier works including reverse indices and ranges like in Python  such as  int   list    1  2  3  4  5  6   var list2   list 2  5  Clone   as int       3  4  5 var list3   list   5  Clone   as int        1  2  3  4  5 var list4   list  4   0  Clone   as int        reverse index

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public   static   T     SubArray lt T gt  T   data  int index  int length                        List lt T gt  retVal   new List lt T gt                 if  data    null    data Length    0                  return retVal ToArray                bool startRead   false              int count   0              for  int i   0  i  lt  data Length  i                                  if  i    index  amp  amp   startRead                      startRead   true                  if  startRead                                         retVal Add data i                        count                         if  count    length                          break                                              return retVal ToArray

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string   arr      Parrot     Snake    Rabbit     Dog     cat      arr   arr ToList   GetRange 0  arr Length -1  ToArray

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There s no single method that will do what you want  You will need to make a clone method available for the class in your array  Then  if LINQ is an option   Foo   newArray   oldArray Skip 3  Take 5  Select item   gt  item Clone    ToArray     class Foo       public Foo Clone                 return  Foo MemberwiseClone

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As far as cloning goes  I don t think serialization calls your constructors  This may break class invariants if you re doing interesting things in the ctor s   It seems the safer bet is virtual clone methods calling copy constructors   protected MyDerivedClass MyDerivedClass myClass              public override MyBaseClass Clone       return new MyDerivedClass this

[c#] How do I clone a range of array elements to a new array?

Below is my original post. It will not work

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