C# Split LIST of double[][]

Question

How to split List2 to 3 lists,

first list 4 items

second list 4 items

third list 2 items

public static class ListExtensions
{
    public static List<List<T>> ChunkBy<T>(this List<T> source, int chunkSize) 
    {
        return source
            .Select((x, i) => new { Index = i, Value = x })
            .GroupBy(x => x.Index / chunkSize)
            .Select(x => x.Select(v => v.Value).ToList())
            .ToList();
    }
}

double[][] x;
x = new double[10][];
   for (int ii = 0; ii < 10; ii++)
   {
         x[ii] = new double[4];
         for (int jj = 0; jj < 4; ++jj)
                 x[ii][jj] = 0.45;
   }

// Convert x matrix to list

 List<double[][]> List2= new List<double[][]>();
 List2.Add(x);

 List<double[][]> List1 = new List<double[][]>();

 List1 = ListExtensions.ChunkBy(List2, 3)[0]; // must be List of double[][]

 Console.Write(List1.Count );  // it should be 3
 Console.ReadLine();

List1 should includes 3 lists of double[][], but i have got one list,

List1.Count : 1

List1 shoulde be like this:

List1[0] = x[0],  x[1],  x[2],  x[3]

List1[1] = x[4],  x[5],  x[6],  x[7]

List2[2] = x[8],  x[9]

Possible duplicate of [Split a List into smaller lists of N size](https://stackoverflow.com/questions/11463734/split-a-list-into-smaller-lists-of-n-size) — Roman Koliada, Dec 15 '17 at 09:28
@RomanKoliada No it is different, part of my answer from your link — shdotcom, Dec 15 '17 at 09:30
This operation also called BATCH: https://stackoverflow.com/questions/13731796/create-batches-in-linq — eocron, Dec 15 '17 at 09:31
@shdotcom How can `List1` contains 3 items if your original `List2` contains only one item? — Roman Koliada, Dec 15 '17 at 09:33
Your list, 'List2' on which you are calling ChunkBy() has only 1 element. — Srinath Mandava, Dec 15 '17 at 09:33
@RomanKoliada I have edited the question, would you please check it. — shdotcom, Dec 15 '17 at 09:52
@shdotcom I guess I finally understand what you want but your `List1` must be of type `List` — Roman Koliada, Dec 15 '17 at 10:55
@RomanKoliada , in my code I have double[][] x and I want to split it to List, the size of x is not constant, the number of arrays in each list also not constant, for example if i want two lists the output will be: List1[0] = x[0], x[1], x[2], x[3], x[4] List1[1] = x[5], x[6], x[7], x[8], x[9] List1 must be: List and i do not want to use skip take method — shdotcom, Dec 15 '17 at 11:19

Roman Koliada · Accepted Answer · 2017-12-15T12:20:07.407

1

I hope this is a function that you need:

List<double[][]> ChunkBy(double[][] x, int number){
    var result = new List<double[][]>();    
    int chunkSize = (int)Math.Ceiling(((double)x.GetLength(0))/number);
    for(int i = 0; i< number; i++){
        result.Add(x.Skip(chunkSize * i).Take(chunkSize).ToArray());    
    }

    return result;
}

edited Dec 15 '17 at 12:20

answered Dec 15 '17 at 11:21

Roman Koliada

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thank you for your help, but the output is not double[][] – shdotcom Dec 15 '17 at 11:54
@shdotcom now it's `double[][]` – Roman Koliada Dec 15 '17 at 12:20
Sorry, I meant List – shdotcom Dec 15 '17 at 13:11
its working, thank you very much, but is it possible to use another method except skip , take? here they mentioned that this method consume a memory [Link](https://stackoverflow.com/questions/11463734/split-a-list-into-smaller-lists-of-n-size) That is why I have used the method provided by **Dmitry Pavlov** in the same link – shdotcom Dec 15 '17 at 13:40
I think `GroupBy` is not more effective than 'Skip().Take()' in your case – Roman Koliada Dec 15 '17 at 13:52

C# Split LIST of double[][]

1 Answers1