How to split an array into chunks of specific size? [closed]

Question

Afternoon,

I need to split an array into smaller "chunks".

I am passing over about 1200 items, and need to split these into easier to handle arrays of 100 items each, which I then need to process.

Could anyone please make some suggestions?

Answer 1

Array.Copy has been around since 1.1 and does an excellent job of chunking arrays.

string[] buffer;  for(int i = 0; i < source.Length; i+=100) {     buffer = new string[100];     Array.Copy(source, i, buffer, 0, 100);     // process array } 

And to make an extension for it:

public static class Extensions {     public static T[] Slice<T>(this T[] source, int index, int length)     {                T[] slice = new T[length];         Array.Copy(source, index, slice, 0, length);         return slice;     } } 

And to use the extension:

string[] source = new string[] { 1200 items here };  // get the first 100 string[] slice = source.Slice(0, 100); 

Update: I think you might be wanting ArraySegment<> No need for performance checks, because it simply uses the original array as its source and maintains an Offset and Count property to determine the 'segment'. Unfortunately, there isn't a way to retrieve JUST the segment as an array, so some folks have written wrappers for it, like here: ArraySegment - Returning the actual segment C#

ArraySegment<string> segment;  for (int i = 0; i < source.Length; i += 100) {     segment = new ArraySegment<string>(source, i, 100);      // and to loop through the segment     for (int s = segment.Offset; s < segment.Array.Length; s++)     {         Console.WriteLine(segment.Array[s]);     } } 

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Performance of Array.Copy vs Skip/Take vs LINQ

Test method (in Release mode):

static void Main(string[] args) {     string[] source = new string[1000000];     for (int i = 0; i < source.Length; i++)     {         source[i] = "string " + i.ToString();     }      string[] buffer;      Console.WriteLine("Starting stop watch");      Stopwatch sw = new Stopwatch();      for (int n = 0; n < 5; n++)     {         sw.Reset();         sw.Start();         for (int i = 0; i < source.Length; i += 100)         {             buffer = new string[100];             Array.Copy(source, i, buffer, 0, 100);         }          sw.Stop();         Console.WriteLine("Array.Copy: " + sw.ElapsedMilliseconds.ToString());          sw.Reset();         sw.Start();         for (int i = 0; i < source.Length; i += 100)         {             buffer = new string[100];             buffer = source.Skip(i).Take(100).ToArray();         }         sw.Stop();         Console.WriteLine("Skip/Take: " + sw.ElapsedMilliseconds.ToString());          sw.Reset();         sw.Start();         String[][] chunks = source                                         .Select((s, i) => new { Value = s, Index = i })                                         .GroupBy(x => x.Index / 100)                                         .Select(grp => grp.Select(x => x.Value).ToArray())                                         .ToArray();         sw.Stop();         Console.WriteLine("LINQ: " + sw.ElapsedMilliseconds.ToString());     }     Console.ReadLine(); } 

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Results (in milliseconds):

Array.Copy:    15 Skip/Take:  42464 LINQ:         881  Array.Copy:    21 Skip/Take:  42284 LINQ:         585  Array.Copy:    11 Skip/Take:  43223 LINQ:         760  Array.Copy:     9 Skip/Take:  42842 LINQ:         525  Array.Copy:    24 Skip/Take:  43134 LINQ:         638 

Answer 2

You can use LINQ to group all items by the chunk size and create new Arrays afterwards.

// build sample data with 1200 Strings string[] items = Enumerable.Range(1, 1200).Select(i => "Item" + i).ToArray(); // split on groups with each 100 items String[][] chunks = items                     .Select((s, i) => new { Value = s, Index = i })                     .GroupBy(x => x.Index / 100)                     .Select(grp => grp.Select(x => x.Value).ToArray())                     .ToArray();  for (int i = 0; i < chunks.Length; i++) {     foreach (var item in chunks[i])         Console.WriteLine("chunk:{0} {1}", i, item); } 

Note that it's not necessary to create new arrays(needs cpu cycles and memory). You could also use the IEnumerable<IEnumerable<String>> when you omit the two ToArrays.

Here's the running code: http://ideone.com/K7Hn2