Splitting an array using LINQ

Question

I have a collection uni-dimensional like this:

[1,2,4,5.....n]

I would like to convert that collection in a bi-dimensional collection like this:

[[1,2,3],
[4,5,6],
...]

Basically I want to group or split if you want, the array in groups of 'n' members

I can do it with a foreach statement, but I am currently learning LINQ so instead of iterating through all elements and create a new array manually I would like to use the LINQ features (if applicable)

Is there any LINQ function to help me to accomplish this??

I was thinking in the GroupBy or SelectMany I do not know if they will help me though but they might

Any help will be truly appreciate it =) :**

It would be possible to write such a query in pure LINQ in many different ways, but I wouldn't recommend doing that, it would be terribly inefficient. — Jeff Mercado
– Jeff Mercado, Commented May 31, 2012 at 3:21
Does this answer your question? Split List into Sublists with LINQ — chwarr
– chwarr, Commented Dec 6, 2022 at 0:21

Sergey Kalinichenko · Accepted Answer · 2012-06-01 16:05:57Z

22

You can group by the index divided by the batch size, like this:

var batchSize = 3;
var batched = orig
    .Select((Value, Index) => new {Value, Index})
    .GroupBy(p => p.Index/batchSize)
    .Select(g => g.Select(p => p.Value).ToList());

edited Jun 1, 2012 at 16:05

answered May 31, 2012 at 3:31

Sergey Kalinichenko

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1 Comment

Marc L. Over a year ago

I was thinking about how to do this with GroupBy, and couldn't figure how to consider the index... thanks.

Tilak · Accepted Answer · 2012-05-31 03:19:39Z

5

Use MoreLinq.Batch

 var result = inputArray.Batch(n); // n -> batch size

Example

    var inputs = Enumerable.Range(1,10);

    var output = inputs.Batch(3);


    var outputAsArray = inputs.Batch(3).Select(x=>x.ToArray()).ToArray(); //If require as array

answered May 31, 2012 at 3:19

Tilak

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3 Comments

Dmitrii Lobanov Over a year ago

+1 for the link to MoreLinq, thanks! I just want to notice that in some cases we have to embed MoreLinq as a source code instead of compiled dll, e.g. if we use LinqBridge.

Jupaol Over a year ago

This is interesting but i checked the source code and it is done with a foreach

Tilak Over a year ago

Most of the methods use foreach with careful use of yield keyword. For any such requirement i first try to find out existing extensions in MoreLinq, LinqExtensions, etc. If i dont find one, and it make sense, i create my own extension.

user610217 · Accepted Answer · 2012-05-31 03:18:42Z

3

You want Take() and Skip(). These methods will let you split an IEnumerable. Then you can use Concat() to slap them together again.

answered May 31, 2012 at 3:18

user610217

Comments

Carolyn Van Slyck · Accepted Answer · 2012-05-31 03:42:18Z

2

The sample below will split an array into groups of 4 items each.

int[] items = Enumerable.Range(1, 20).ToArray(); // Generate a test array to split
int[][] groupedItems = items
                         .Select((item, index) => index % 4 == 0 ? items.Skip(index).Take(4).ToArray() : null)
                         .Where(group => group != null)
                         .ToArray();

answered May 31, 2012 at 3:42

Carolyn Van Slyck

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Comments

Dmitrii Lobanov · Accepted Answer · 2012-06-01 07:13:44Z

2

It's not a pure LINQ but it's intended to be used with it:

public static class MyEnumerableExtensions
{
    public static IEnumerable<T[]> Split<T>(this IEnumerable<T> source, int size)
    {
        if (source == null)
        {
            throw new ArgumentNullException("source can't be null.");
        }

        if (size == 0)
        {
            throw new ArgumentOutOfRangeException("Chunk size can't be 0.");
        }

        List<T> result = new List<T>(size);
        foreach (T x in source)
        {
            result.Add(x);
            if (result.Count == size)
            {
                yield return result.ToArray();
                result = new List<T>(size);
            }
        }
    }
}

It can be used from your code as:

private void Test()
{
    // Here's your original sequence
    IEnumerable<int> seq = new[] { 1, 2, 3, 4, 5, 6 };

    // Here's the result of splitting into chunks of some length 
    // (here's the chunks length equals 3). 
    // You can manipulate with this sequence further, 
    // like filtering or joining e.t.c.
    var splitted = seq.Split(3);
}

edited Jun 1, 2012 at 7:13

answered May 31, 2012 at 3:19

Dmitrii Lobanov

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4 Comments

Marc L. Over a year ago

A semantic point: "splice" in English actually means "join together", whereas the method is actually pulling the array apart.

gabba Over a year ago

on last step if result.Count < size, last part of source will be lost

Dmitrii Lobanov Over a year ago

@gabba yeah, thanks! I assumed that the initial sequence would consist of k*size elements. I think it would be better to throw an exception if this is not true.

Michael Blackburn Over a year ago

@DmitryLobanov, When in doubt, use "cleave" -- it means both "to split apart" and "to fuse together!" As the saying goes, "English doesn't borrow from other languages. English follows other languages down dark alleys, knocks them over, and rummages through their pockets for loose grammar."

ShloEmi · Accepted Answer · 2016-09-13 14:00:06Z

1

It's as simple as:

static class LinqExtensions
{
    public static IEnumerable<IEnumerable<T>> ToPages<T>(this IEnumerable<T> elements, int pageSize)
    {
        if (elements == null)
            throw new ArgumentNullException("elements");
        if (pageSize <= 0)
            throw new ArgumentOutOfRangeException("pageSize","Must be greater than 0!");

        int i = 0;
        var paged = elements.GroupBy(p => i++ / pageSize);
        return paged;
    }
}

edited Sep 13, 2016 at 14:00

answered Sep 13, 2016 at 13:43

ShloEmi

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Comments

chwarr · Accepted Answer · 2022-12-06 00:17:21Z

1

Starting with .NET 6, there is the System.Linq.Enumerable.Chunk(this IEnumerable<TSource>, int size) extension method. It returns an IEnumerable<TSource[]> where each item is an array of size elements, except the last item, which could have fewer.

Code like this:

using System;
using System.Collections.Generic;
using System.Linq;

int[] input = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

IEnumerable<int[]> chunks = input.Chunk(3);

foreach (int[] chunk in chunks)
{
    foreach (int i in chunk)
    {
        Console.Write($"{i} ");
    }
    
    Console.WriteLine();
}

outputs

answered Dec 6, 2022 at 0:17

chwarr

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Comments

DaemonFire · Accepted Answer · 2020-01-11 16:04:19Z

0

I based my solution of Jeremy Holovacs's answer and used Take() and Skip() to create subarrays.

        const int batchSize = 3;
        int[] array = new int[] { 1,2,4,5.....n};

        var subArrays = from index in Enumerable.Range(0, array.Length / batchSize + 1)
                      select array.Skip(index * batchSize).Take(batchSize);

edited Jan 11, 2020 at 16:04

answered Jan 11, 2020 at 15:53

DaemonFire

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