Add new item in existing array in c net

Question

How to add new item in existing string array in C  net   I need to preserve the existing data

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Why not try out using the Stringbuilder class  It has methods such as  insert and  append  You can read more about it here  http   msdn microsoft com en-us library 2839d5h5 v vs 71  aspx

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Arrays in C  are immutable  e g  string    int    That means you can t resize them  You need to create a brand new array   Here is the code for Array Resize   public static void Resize lt T gt  ref T   array  int newSize        if  newSize  lt  0                throw new ArgumentOutOfRangeException  newSize   Environment GetResourceString  ArgumentOutOfRange NeedNonNegNum               T   sourceArray   array      if  sourceArray    null                array   new T newSize             else if  sourceArray Length    newSize                T   destinationArray   new T newSize           Copy sourceArray  0  destinationArray  0   sourceArray Length  gt  newSize    newSize   sourceArray Length           array   destinationArray            As you can see it creates a new array with the new size  copies the content of the source array and sets the reference to the new array  The hint for this is the ref keyword for the first parameter   There are lists that can dynamically allocate new slots for new items  This is e g  List lt T   These contain immutable arrays and resize them when needed  List lt T  is not a linked list implementation    ArrayList is the same thing without Generics  with Object array    LinkedList lt T  is a real linked list implementation  Unfortunately you can add just LinkListNode lt T  elements to the list  so you must wrap your own list elements into this node type  I think its use is uncommon

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That could be a solution   Array Resize ref array  newsize   array newsize - 1     newvalue    But for dynamic sized array I would prefer list too

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So if you have a existing array  my quick fix will be  var tempList   originalArray ToList    tempList Add newitem     Now just replace the original array with the new one  originalArray   tempList ToArray

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Using a list would be your best option for memory management

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Very old question  but still wanted to add this   If you re looking for a one-liner  you can use the code below  It combines the list constructor that accepts an enumerable and the  new   since question raised  initializer syntax   myArray   new List lt string gt  myArray     add this    ToArray

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A new Append lt TSource gt  method has been added to IEnumerable lt TSource gt  since  NET Framework 4 7 1 and  NET Core 1 0   Here is how to use it   var numbers   new       one    two    three     numbers   numbers Append  four   ToArray    Console WriteLine string Join       numbers       one  two  three  four   Note that if you want to add the element at the beginning of the array  you can use the new Prepend lt TSource gt  method instead

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That could be a solution   Array Resize ref array  newsize   array newsize - 1     newvalue    But for dynamic sized array I would prefer list too

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I would use a List if you need a dynamically sized array   List lt string gt  ls   new List lt string gt     ls Add  Hello

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Arrays in C  are immutable  e g  string    int    That means you can t resize them  You need to create a brand new array   Here is the code for Array Resize   public static void Resize lt T gt  ref T   array  int newSize        if  newSize  lt  0                throw new ArgumentOutOfRangeException  newSize   Environment GetResourceString  ArgumentOutOfRange NeedNonNegNum               T   sourceArray   array      if  sourceArray    null                array   new T newSize             else if  sourceArray Length    newSize                T   destinationArray   new T newSize           Copy sourceArray  0  destinationArray  0   sourceArray Length  gt  newSize    newSize   sourceArray Length           array   destinationArray            As you can see it creates a new array with the new size  copies the content of the source array and sets the reference to the new array  The hint for this is the ref keyword for the first parameter   There are lists that can dynamically allocate new slots for new items  This is e g  List lt T   These contain immutable arrays and resize them when needed  List lt T  is not a linked list implementation    ArrayList is the same thing without Generics  with Object array    LinkedList lt T  is a real linked list implementation  Unfortunately you can add just LinkListNode lt T  elements to the list  so you must wrap your own list elements into this node type  I think its use is uncommon

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I would use a List if you need a dynamically sized array   List lt string gt  ls   new List lt string gt     ls Add  Hello

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I agree with Ed   C  does not make this easy the way VB does with ReDim Preserve   Without a collection  you ll have to copy the array into a larger one

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I agree with Ed   C  does not make this easy the way VB does with ReDim Preserve   Without a collection  you ll have to copy the array into a larger one

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All proposed answers do the same as what they say they d like to avoid  creating a new array and adding a new entry in it only with lost more overhead   LINQ is not magic  list of T is an array with a buffer space with some extra space as to avoid resizing the inner array when items are added    All the abstractions have to solve the same issue  create an array with no empty slots that hold all values and return them    If you need the flexibility an can create a large enough list that you can use to pass then do that  else use an array and share that thread-safe object  Also  the new Span helps to share data without having to copy the lists around     To answer the question   Array Resize ref myArray  myArray Length   1   data myArray Length - 1    Value

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Since this question not satisfied  with provided answer  I would like to add this answer     public class CustomArrayList lt T gt           private T   arr   private int count     public int Count              get                        return this count                       private const int INITIAL CAPACITY   4      public CustomArrayList int capacity   INITIAL CAPACITY            this arr   new T capacity     this count   0          public void Add T item             GrowIfArrIsFull         this arr this count    item   this count            public void Insert int index  T item        if  index  gt  this count    index  lt  0                   throw new IndexOutOfRangeException      Invalid index      index                   GrowIfArrIsFull           Array Copy this arr  index    this arr  index   1  this count - index                 this arr index    item   this count             private void GrowIfArrIsFull                if  this count   1  gt  this arr Length                   T   extendedArr   new T this arr Length   2           Array Copy this arr  extendedArr  this count           this arr   extendedArr

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So if you have a existing array  my quick fix will be  var tempList   originalArray ToList    tempList Add newitem     Now just replace the original array with the new one  originalArray   tempList ToArray

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It s better to keeps Array immutable and fixed size   you can simulate Add by Extension Method and IEnumerable Concat    public static class ArrayExtensions               public static string   Add this string   array  string item                        return array Concat new    item   ToArray

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I would use a List if you need a dynamically sized array   List lt string gt  ls   new List lt string gt     ls Add  Hello

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I agree with Ed   C  does not make this easy the way VB does with ReDim Preserve   Without a collection  you ll have to copy the array into a larger one

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It s better to keeps Array immutable and fixed size   you can simulate Add by Extension Method and IEnumerable Concat    public static class ArrayExtensions               public static string   Add this string   array  string item                        return array Concat new    item   ToArray

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That could be a solution   Array Resize ref array  newsize   array newsize - 1     newvalue    But for dynamic sized array I would prefer list too

User · Answer

A new Append lt TSource gt  method has been added to IEnumerable lt TSource gt  since  NET Framework 4 7 1 and  NET Core 1 0   Here is how to use it   var numbers   new       one    two    three     numbers   numbers Append  four   ToArray    Console WriteLine string Join       numbers       one  two  three  four   Note that if you want to add the element at the beginning of the array  you can use the new Prepend lt TSource gt  method instead

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Using a list would be your best option for memory management

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You can expand on the answer provided by  Stephen Chung by using his LINQ based logic to create an extension method using a generic type   public static class CollectionHelper       public static IEnumerable lt T gt  Add lt T gt  this IEnumerable lt T gt  sequence  T item                return  sequence    Enumerable Empty lt T gt     Concat new     item                public static T   AddRangeToArray lt T gt  this T   sequence  T   items                return  sequence    Enumerable Empty lt T gt     Concat items  ToArray               public static T   AddToArray lt T gt  this T   sequence  T item                return Add sequence  item  ToArray               You can then call it directly on the array like this       public void AddToArray string   options                   Add one item         options   options AddToArray  New Item                Add a          options   options AddRangeToArray new string      one    two    three                  Do stuff            Admittedly  the AddRangeToArray   method seems a bit overkill since you have the same functionality with Concat   but this way the end code can  work  with the array directly as opposed to this   options   options Concat new string      one    two    three     ToArray

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Unfortunately using a list won t work in all situations  A list and an array are actually different and are not 100  interchangeable  It would depend on the circumstances if this would be an acceptable work around

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What about using an extension method   For instance   public static IEnumerable lt TSource gt  Union lt TSource gt  this IEnumerable lt TSource gt  source  TSource item        return source Union new TSource     item         for instance   string   sourceArray   new           foo        bar    string additionalItem    foobar   string result   sourceArray Union additionalItem     Note this mimics this behavior of Linq s Uniion extension  used to combine two arrays into a new one   and required the Linq library to function

User · Answer

All proposed answers do the same as what they say they d like to avoid  creating a new array and adding a new entry in it only with lost more overhead   LINQ is not magic  list of T is an array with a buffer space with some extra space as to avoid resizing the inner array when items are added    All the abstractions have to solve the same issue  create an array with no empty slots that hold all values and return them    If you need the flexibility an can create a large enough list that you can use to pass then do that  else use an array and share that thread-safe object  Also  the new Span helps to share data without having to copy the lists around     To answer the question   Array Resize ref myArray  myArray Length   1   data myArray Length - 1    Value

User · Answer

You can expand on the answer provided by  Stephen Chung by using his LINQ based logic to create an extension method using a generic type   public static class CollectionHelper       public static IEnumerable lt T gt  Add lt T gt  this IEnumerable lt T gt  sequence  T item                return  sequence    Enumerable Empty lt T gt     Concat new     item                public static T   AddRangeToArray lt T gt  this T   sequence  T   items                return  sequence    Enumerable Empty lt T gt     Concat items  ToArray               public static T   AddToArray lt T gt  this T   sequence  T item                return Add sequence  item  ToArray               You can then call it directly on the array like this       public void AddToArray string   options                   Add one item         options   options AddToArray  New Item                Add a          options   options AddRangeToArray new string      one    two    three                  Do stuff            Admittedly  the AddRangeToArray   method seems a bit overkill since you have the same functionality with Concat   but this way the end code can  work  with the array directly as opposed to this   options   options Concat new string      one    two    three     ToArray

User · Answer

That could be a solution   Array Resize ref array  newsize   array newsize - 1     newvalue    But for dynamic sized array I would prefer list too

User · Answer

Unfortunately using a list won t work in all situations  A list and an array are actually different and are not 100  interchangeable  It would depend on the circumstances if this would be an acceptable work around

User · Answer

I would use a List if you need a dynamically sized array   List lt string gt  ls   new List lt string gt     ls Add  Hello

User · Answer

Since this question not satisfied  with provided answer  I would like to add this answer     public class CustomArrayList lt T gt           private T   arr   private int count     public int Count              get                        return this count                       private const int INITIAL CAPACITY   4      public CustomArrayList int capacity   INITIAL CAPACITY            this arr   new T capacity     this count   0          public void Add T item             GrowIfArrIsFull         this arr this count    item   this count            public void Insert int index  T item        if  index  gt  this count    index  lt  0                   throw new IndexOutOfRangeException      Invalid index      index                   GrowIfArrIsFull           Array Copy this arr  index    this arr  index   1  this count - index                 this arr index    item   this count             private void GrowIfArrIsFull                if  this count   1  gt  this arr Length                   T   extendedArr   new T this arr Length   2           Array Copy this arr  extendedArr  this count           this arr   extendedArr

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Arrays in C  are immutable  e g  string    int    That means you can t resize them  You need to create a brand new array   Here is the code for Array Resize   public static void Resize lt T gt  ref T   array  int newSize        if  newSize  lt  0                throw new ArgumentOutOfRangeException  newSize   Environment GetResourceString  ArgumentOutOfRange NeedNonNegNum               T   sourceArray   array      if  sourceArray    null                array   new T newSize             else if  sourceArray Length    newSize                T   destinationArray   new T newSize           Copy sourceArray  0  destinationArray  0   sourceArray Length  gt  newSize    newSize   sourceArray Length           array   destinationArray            As you can see it creates a new array with the new size  copies the content of the source array and sets the reference to the new array  The hint for this is the ref keyword for the first parameter   There are lists that can dynamically allocate new slots for new items  This is e g  List lt T   These contain immutable arrays and resize them when needed  List lt T  is not a linked list implementation    ArrayList is the same thing without Generics  with Object array    LinkedList lt T  is a real linked list implementation  Unfortunately you can add just LinkListNode lt T  elements to the list  so you must wrap your own list elements into this node type  I think its use is uncommon

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Array Resize ref youur array name  your array name Length   1    your array name your array name Length - 1     new item

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Array Resize ref youur array name  your array name Length   1    your array name your array name Length - 1     new item

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Using LINQ   arr    arr    Enumerable Empty lt string gt     Concat new     newitem    ToArray      I like using this as it is a one-liner and very convenient to embed in a switch statement  a simple if-statement  or pass as argument   EDIT   Some people don t like new     newitem   because it creates a small  one-item  temporary array   Here is a version using Enumerable Repeat that does not require creating any object  at least not on the surface --  NET iterators probably create a bunch of state machine objects under the table    arr    arr    Enumerable Empty lt string gt     Concat Enumerable Repeat newitem 1   ToArray      And if you are sure that the array is never null to start with  you can simplify it to   arr Concat Enumerable Repeat newitem 1   ToArray      Notice that if you want to add items to a an ordered collection  List is probably the data structure you want  not an array to start with

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private static string   GetMergedArray string   originalArray  string   newArray                int startIndexForNewArray   originalArray Length          Array Resize lt string gt  ref originalArray  originalArray Length   newArray Length           newArray CopyTo originalArray  startIndexForNewArray           return originalArray

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string str    string    List lt string gt  li str   new List lt string gt         for  int k   0  k  lt  100  i              li str Add str k ToString     string   arr str   li str ToArray

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if you are working a lot with arrays and not lists for some reason  this generic typed return generic method Add might help      public static T   Add lt T gt  T   array  T item                T   returnarray   new T array Length   1           for  int i   0  i  lt  array Length  i                          returnarray i    array i                     returnarray array Length    item          return returnarray

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Using LINQ   arr    arr    Enumerable Empty lt string gt     Concat new     newitem    ToArray      I like using this as it is a one-liner and very convenient to embed in a switch statement  a simple if-statement  or pass as argument   EDIT   Some people don t like new     newitem   because it creates a small  one-item  temporary array   Here is a version using Enumerable Repeat that does not require creating any object  at least not on the surface --  NET iterators probably create a bunch of state machine objects under the table    arr    arr    Enumerable Empty lt string gt     Concat Enumerable Repeat newitem 1   ToArray      And if you are sure that the array is never null to start with  you can simplify it to   arr Concat Enumerable Repeat newitem 1   ToArray      Notice that if you want to add items to a an ordered collection  List is probably the data structure you want  not an array to start with

User · Answer

What about using an extension method   For instance   public static IEnumerable lt TSource gt  Union lt TSource gt  this IEnumerable lt TSource gt  source  TSource item        return source Union new TSource     item         for instance   string   sourceArray   new           foo        bar    string additionalItem    foobar   string result   sourceArray Union additionalItem     Note this mimics this behavior of Linq s Uniion extension  used to combine two arrays into a new one   and required the Linq library to function

User · Answer

Arrays in C  are immutable  e g  string    int    That means you can t resize them  You need to create a brand new array   Here is the code for Array Resize   public static void Resize lt T gt  ref T   array  int newSize        if  newSize  lt  0                throw new ArgumentOutOfRangeException  newSize   Environment GetResourceString  ArgumentOutOfRange NeedNonNegNum               T   sourceArray   array      if  sourceArray    null                array   new T newSize             else if  sourceArray Length    newSize                T   destinationArray   new T newSize           Copy sourceArray  0  destinationArray  0   sourceArray Length  gt  newSize    newSize   sourceArray Length           array   destinationArray            As you can see it creates a new array with the new size  copies the content of the source array and sets the reference to the new array  The hint for this is the ref keyword for the first parameter   There are lists that can dynamically allocate new slots for new items  This is e g  List lt T   These contain immutable arrays and resize them when needed  List lt T  is not a linked list implementation    ArrayList is the same thing without Generics  with Object array    LinkedList lt T  is a real linked list implementation  Unfortunately you can add just LinkListNode lt T  elements to the list  so you must wrap your own list elements into this node type  I think its use is uncommon

User · Answer

I agree with Ed   C  does not make this easy the way VB does with ReDim Preserve   Without a collection  you ll have to copy the array into a larger one

User · Answer

Very old question  but still wanted to add this   If you re looking for a one-liner  you can use the code below  It combines the list constructor that accepts an enumerable and the  new   since question raised  initializer syntax   myArray   new List lt string gt  myArray     add this    ToArray

User · Answer

if you are working a lot with arrays and not lists for some reason  this generic typed return generic method Add might help      public static T   Add lt T gt  T   array  T item                T   returnarray   new T array Length   1           for  int i   0  i  lt  array Length  i                          returnarray i    array i                     returnarray array Length    item          return returnarray

User · Answer

Why not try out using the Stringbuilder class  It has methods such as  insert and  append  You can read more about it here  http   msdn microsoft com en-us library 2839d5h5 v vs 71  aspx

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private static string   GetMergedArray string   originalArray  string   newArray                int startIndexForNewArray   originalArray Length          Array Resize lt string gt  ref originalArray  originalArray Length   newArray Length           newArray CopyTo originalArray  startIndexForNewArray           return originalArray

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string str    string    List lt string gt  li str   new List lt string gt         for  int k   0  k  lt  100  i              li str Add str k ToString     string   arr str   li str ToArray

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