109

7
+4  Q:

## Divide array into an array of subsequence array

I have a byte array:

byte[] bytes; // many elements

I need to divide it into subsequence of byte arrays of X elements. For example, x = 4.

If bytes.Length does not multiply by X, then add 0 to last subsequence array so Length of all subsequnce must be X.

Linq available.

PS: my attempts

``````    static void Main(string[] args)
{
List<byte> bytes = new List<byte>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };

int c = bytes.Count / 4;

for (int i = 0; i <= c; i+=4)
{
int diff = bytes.Count - 4;

if (diff < 0)
{

}
else
{
List<byte> b = bytes.GetRange(i, 4);
}
}

Console.ReadKey();
}
``````
+1  A:
``````    const int x = 4;
var bytes = new List<byte>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
var groups = bytes.Select((b, index) => new { b, index }).GroupBy(obj => obj.index / x).Select(group => new List<byte>(group.Select(i => i.b)));
var last = groups.Last();
while (last.Count < x)
{
last.Add(0);
}
``````
A nice solution, but note that it is forced to buffer the entire sequence first - this *may* be perfectly fine in most common cases.
+6  A:

This is quite cute:

``````static class ChunkExtension
{
public static IEnumerable<T[]> Chunkify<T>(
this IEnumerable<T> source, int size)
{
if (source == null) throw new ArgumentNullException("source");
if (size < 1) throw new ArgumentOutOfRangeException("size");
using (var iter = source.GetEnumerator())
{
while (iter.MoveNext())
{
var chunk = new T[size];
chunk[0] = iter.Current;
for (int i = 1; i < size && iter.MoveNext(); i++)
{
chunk[i] = iter.Current;
}
yield return chunk;
}
}
}
}
static class Program
{
static void Main(string[] args)
{
List<byte> bytes = new List<byte>() {
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
var chunks = bytes.Chunkify(4);
foreach (byte[] chunk in chunks)
{
foreach (byte b in chunk) Console.Write(b.ToString("x2") + " ");
Console.WriteLine();
}
}
}
``````
great! thank you
+1  A:

You could try this:

``````    List<byte> bytes = new List<byte>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };

int partLength = 4;
int c = bytes.Count / partLength;

if((c % partLength) != 0)
c++; // we need one last list which will have to be filled with 0s

List<List<byte>> allLists = new List<List<byte>>();

for (int i = 0; i <= c; i++)
allLists.Add(bytes.Take(partLength).ToList());

int zerosNeeded = partLength - allLists.Last().Count;

for (int i = 0; i < zerosNeeded; i++)
allLists.Last().Add(0);
``````

Ask if anything is unclear.

+1  A:

How about this:

``````var bytes = new List<byte>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };

var result = Chunkify(bytes, 4);

IEnumerable<IEnumerable<T>> Chunkify<T>(IEnumerable<T> source, int chunkSize)
{
var indicies =
Enumerable.Range(0, source.Count()).Where(i => i%chunkSize==0);

var chunks =
indicies
.Select( i => source.Skip(i).Take(chunkSize) )
.Select( chunk => new { Chunk=chunk, Count=chunk.Count() } )
.Select( c => c.Count < chunkSize ? c.Chunk.Concat( Enumerable.Repeat( default(T), chunkSize - c.Count ) ) : c.Chunk )
;

return chunks;
}
``````
A:
``````//without LINQ

List<byte> bytes = new List<byte>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
int x = 4;
int initialLength = bytes.Count;
for (int i = 0; i < (x - (initialLength % x)); i++) // adds enough 0's to list
{
bytes.Add(0);
}

List<byte[]> byteList= new List<byte[]>(); // contains answers

for (int i=0;i<bytes.Count;i+=4)
{
byteList.Add(bytes.GetRange(i,4).ToArray());
}
``````
A:

You'll want to take Marc Gravell's solution of course, but I couldn't resist hacking together a pure LINQ version, just to see if it can be done:

``````static IEnumerable<T[]> LinqChunks<T>(IEnumerable<T> input, int chunkSize)
{
return input
//assign chunk numbers to elements by integer division
.Select((x, index) => new {ChunkNr = index / chunkSize, Value = x})

//group by chunk number
.GroupBy(item => item.ChunkNr)

//convert chunks to arrays, and pad with zeroes if necessary
.Select(group =>
{
var block = group.Select(item => item.Value).ToArray();

//if block size = chunk size -> return the block
if (block.Length == chunkSize) return block;

//if block size < chunk size -> this is the last block, pad it
var lastBlock= new T[chunkSize];
for (int i = 0; i < block.Length; i++) lastBlock[i] = block[i];
return lastBlock;
});
}
``````
A:

And if somebody wants purely functional solution -

``````static IEnumerable<T[]> Chunkify<T>(IEnumerable<T> input, int size)
{
return input
.Concat(Enumerable.Repeat(default(T), size - input.Count() % size))
.Select((x, i) => new { Value = x, Chunk = i / size })
.GroupBy(x => x.Chunk, x => x.Value)
.Select(x => x.ToArray());
}
``````