Merging two arrays in NET

Question

Is there a built in function in  NET 2 0 that will take two arrays and merge them into one array   The arrays are both of the same type  I m getting these arrays from a widely used function within my code base and can t modify the function to return the data in a different format   I m looking to avoid writing my own function to accomplish this if possible

User · Answer

If you have the source arrays in an array itself you can use SelectMany:

var arrays = new[]{new[]{1, 2, 3}, new[]{4, 5, 6}};
var combined = arrays.SelectMany(a => a).ToArray();
foreach (var v in combined) Console.WriteLine(v);

gives

Probably this is not the fastest method but might fit depending on usecase.

User · Answer

Created and extension method to handle null  public static class IEnumerableExtenions       public static IEnumerable lt T gt  UnionIfNotNull lt T gt  this IEnumerable lt T gt  list1  IEnumerable lt T gt  list2                if  list1    null  amp  amp  list2    null              return list1 Union list2           else if  list1    null              return list1          else if  list2    null              return list2          else return null

User · Answer

In C  3 0 you can use LINQ s Concat method to accomplish this easily   int   front     1  2  3  4    int   back     5  6  7  8    int   combined   front Concat back  ToArray      In C  2 0 you don t have such a direct way  but Array Copy is probably the best solution   int   front     1  2  3  4    int   back     5  6  7  8     int   combined   new int front Length   back Length   Array Copy front  combined  front Length   Array Copy back  0  combined  front Length  back Length     This could easily be used to implement your own version of Concat

User · Answer

Use LINQ   var arr1   new     1  2  3  4  5    var arr2   new     6  7  8  9  0    var arr   arr1 Union arr2  ToArray      Keep in mind  this will remove duplicates  If you want to keep duplicates  use Concat

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Just to have it noted as an option  if the arrays you are working with are of a primitive type  ndash  Boolean  bool   Char  SByte  Byte  Int16  short   UInt16  Int32  int   UInt32  Int64  long   UInt64  IntPtr  UIntPtr  Single  or Double  ndash  then you could  or should   try using Buffer BlockCopy  According to the MSDN page for the Buffer class      This class provides better performance for manipulating primitive types than similar methods in the System Array class    Using the C  2 0 example from  OwenP s answer as a starting point  it would work as follows   int   front     1  2  3  4    int   back     5  6  7  8     int   combined   new int front Length   back Length   Buffer BlockCopy front  0  combined  0  front Length   Buffer BlockCopy back  0  combined  front Length  back Length     There is barely any difference in syntax between Buffer BlockCopy and the Array Copy that  OwenP used  but this should be faster  even if only slightly

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I needed a solution to combine an unknown number of arrays   Surprised nobody else provided a solution using SelectMany with params     private static T   Combine lt T gt  params IEnumerable lt T gt    items    gt                      items SelectMany i   gt  i  Distinct   ToArray      If you don t want distinct items just remove distinct    public string   Reds   new       Red    Crimson    TrafficLightRed      public string   Greens   new       Green    LimeGreen      public string   Blues   new       Blue    SkyBlue    Navy       public string   Colors   Combine Reds  Greens  Blues     Note  There is definitely no guarantee of ordering when using distinct

User · Answer

If you don t want to remove duplicates  then try this  Use LINQ   var arr1   new     1  2  3  4  5    var arr2   new     6  7  8  9  0    var arr   arr1 Concat arr2  ToArray

User · Answer

Everyone has already had their say but I think this more readable than the  use as Extension method  approach   var arr1   new     1  2  3  4  5    var arr2   new     6  7  8  9  0    var arr   Queryable Concat arr1  arr2  ToArray      However it can only be used when bringing together 2 arrays

User · Answer

Try this   ArrayLIst al   new ArrayList    al AddRange array 1   al AddRange array 2   al AddRange array 3   array 4   al ToArray

User · Answer

I think you can use Array Copy for this  It takes a source index and destination index so you should be able to append the one array to the other  If you need to go more complex than just appending one to the other  this may not be the right tool for you

User · Answer

First  make sure you ask yourself the question  Should I really be using an Array here    Unless you re building something where speed is of the utmost importance  a typed List  like List lt int gt  is probably the way to go  The only time I ever use arrays are for byte arrays when sending stuff over the network  Other than that  I never touch them

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This is what I came up with  Works for a variable number of arrays    public static T   ConcatArrays lt T gt  params T     args                if  args    null              throw new ArgumentNullException             var offset   0          var newLength   args Sum arr   gt  arr Length            var newArray   new T newLength            foreach  var arr in args                        Buffer BlockCopy arr  0  newArray  offset  arr Length               offset    arr Length                     return newArray                  var header   new byte     0  1  2   var data   new byte     3  4  5  6    var checksum   new byte    7  0   var newArray   ConcatArrays header  data  checksum     output byte 9    0  1  2  3  4  5  6  7  0

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This code will work for all cases   int   a1   3 4 5 6   int   a2    4 7 9   int i   a1 Length-1  int j   a2 Length-1  int resultIndex   i j 1  Array Resize ref a2  a1 Length  a2 Length   while resultIndex  gt  0        if i    0  amp  amp  j   0                if a1 i   gt  a2 j                         a2 resultIndex--    a i--                     else                       a2 resultIndex--    a j--                       else if i gt  0  amp  amp  j lt  0                 a2 resultIndex--    a i--             else if j gt  0  amp  amp  i  lt  0               a2 resultIndex--    a j--

User · Answer

Easier would just be using LINQ   var array   new string      test    ToList    var array1   new string      test    ToList    array AddRange array1   var result   array ToArray      First convert the arrays to lists and merge them    After that just convert the list back to an array

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In case someone else is looking for how to merge two image byte arrays           private void LoadImage                         string src   string empty              byte   mergedImageData   new byte 0                mergedImageData   MergeTwoImageByteArrays watermarkByteArray  backgroundImageByteArray               src    data image png base64     Convert ToBase64String mergedImageData               MyImage ImageUrl   src                     private byte   MergeTwoImageByteArrays byte   imageBytes  byte   imageBaseBytes                        byte   mergedImageData   new byte 0               using  var msBase   new MemoryStream imageBaseBytes                                 System Drawing Image imgBase   System Drawing Image FromStream msBase                   Graphics gBase   Graphics FromImage imgBase                   using  var msInfo   new MemoryStream imageBytes                                         System Drawing Image imgInfo   System Drawing Image FromStream msInfo                       Graphics gInfo   Graphics FromImage imgInfo                       gBase DrawImage imgInfo  new Point 0  0                          imgBase Save Server MapPath       testImg png    ImageFormat Png                       MemoryStream mergedImageStream   new MemoryStream                        imgBase Save mergedImageStream  ImageFormat Png                       mergedImageData   mergedImageStream ToArray                        mergedImageStream Close                                                return mergedImageData

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Personally  I prefer my own Language Extensions  which I add or remove at will for rapid prototyping   Following is an example for strings     resides in IEnumerableStringExtensions cs public static class IEnumerableStringExtensions      public static IEnumerable lt string gt  Append this string   arrayInitial  string   arrayToAppend              string   ret   new string arrayInitial Length   arrayToAppend Length          arrayInitial CopyTo ret  0          arrayToAppend CopyTo ret  arrayInitial Length           return ret           It is much faster than LINQ and Concat  Faster still  is using a custom IEnumerable Type-wrapper which stores references pointers of passed arrays and allows looping over the entire collection as if it were a normal array   Useful in HPC  Graphics Processing  Graphics render      Your Code   var someStringArray   new    a    b    c    var someStringArray2   new    d    e    f    someStringArray Append someStringArray2      contains a b c d e f   For the entire code and a generics version see  https   gist github com lsauer 7919764  Note  This returns an unextended IEnumerable object  To return an extended object is a bit slower   I compiled such extensions since 2002  with a lot of credits going to helpful people on CodeProject and  Stackoverflow   I will release these shortly and put the link up here

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I m assuming you re using your own array types as opposed to the built-in  NET arrays   public string   merge input1  input2        string   output   new string input1 length   input2 length       for int i   0  i  lt  output length  i                  if  i  gt   input1 length              output i    input2 i-input1 length           else             output i    input1 i             return output      Another way of doing this would be using the built in ArrayList class   public ArrayList merge input1  input2        Arraylist output   new ArrayList        foreach string val in input1          output add val       foreach string val in input2          output add val       return output      Both examples are C

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Here is a simple example using Array CopyTo  I think that it answers your question and gives an example of CopyTo usage - I am always puzzled when I need to use this function because the help is a bit unclear - the index is the position in the destination array where inserting occurs   int   xSrc1   new int 3    0  1  2    int   xSrc2   new int 5    3  4  5  6   7     int   xAll   new int xSrc1 Length   xSrc2 Length   xSrc1 CopyTo xAll  0   xSrc2 CopyTo xAll  xSrc1 Length     I guess you can t get it much simpler

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int    SouceArray1   new int    2 1 3   int    SourceArray2   new int    4 5 6   int    targetArray   new int  SouceArray1 Length   SourceArray2 Length   SouceArray1 CopyTo targetArray 0   SourceArray2 CopyTo targetArray SouceArray1 Length     foreach  int i in targetArray  Console WriteLine i             Using the above code two Arrays can be easily merged

User · Answer

Assuming the destination array has enough space  Array Copy   will work  You might also try using a List lt T gt  and its  AddRange   method

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If you can manipulate one of the arrays  you can resize it before performing the copy   T   array1   getOneArray    T   array2   getAnotherArray    int array1OriginalLength   array1 Length  Array Resize lt T gt  ref array1  array1OriginalLength   array2 Length   Array Copy array2  0  array1  array1OriginalLength  array2 Length     Otherwise  you can make a new array  T   array1   getOneArray    T   array2   getAnotherArray    T   newArray   new T array1 Length   array2 Length   Array Copy array1  newArray  array1 Length   Array Copy array2  0  newArray  array1 Length  array2 Length     More on available Array methods on MSDN

[c#] Merging two arrays in .NET

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