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BillWoodruff

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15 Oct 2021CPOL

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Create collections of #n sized elements from arrays, lists, and string

This is an extension method that returns an IEnumerable<T> containing #n groups of Type T elements of arrays, lists, and string. In the case of a string: returns an IEnumerable<Char>

In a recent Insider News story, Bite-size-NET-6-Chunk-in-LINQ, the new Chunk features in .NET 6 are discussed. We are mere mortals that don't use the EF database context/pagination functions... have been chunking a long time; my version works with lists/arrays of any type, including DateTime, TimeSpan and single strings (returns chunks of Type Char):

//
// required
using System;
using System.Collections.Generic;
using System.Linq;

public static class ChunkExtensions
{
    public static IEnumerable<List<T>> GetChunks<T>(this IEnumerable<T> source, int chunksize)
    {
        int cnt = source.Count();

        if (cnt == 0) yield return null;

        // required to enable 'GetRange
        List<T> slist = source.ToList();

        if (chunksize <= 0 || chunksize >= cnt) //  alternative ? throw error
        {
            yield return slist;
            yield break;
        }
        
        int rem = cnt % chunksize;
        int lastchunkstart = cnt - rem;

        for (int i = 0; i < lastchunkstart; i += chunksize)
        {
            yield return slist.GetRange(i, chunksize);
        }

        if (rem > 0)
        {
            yield return slist.GetRange(lastchunkstart, rem);
        }
    }
}

// usage example

List<int> ints = Enumerable.Range(0, 100).ToList();

List<List<int>> chunk27 = ints.GetChunks(27).ToList();

for (int i = 0; i < chunk27.Count; i++)
{
    List<int> chunk = chunk27[i];
    Console.WriteLine($"chunk {i} : #items {chunk.Count}");
}

// output:

chunk 0 : #items 27
chunk 1 : #items 27
chunk 2 : #items 27
chunk 3 : #items 19

History

16^th October, 2021: Initial version

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

BillWoodruff

Chief Technology Officer

Thailand

Human being, mortal, flawed.

List<T> chunk = new List<T>(chunksize); foreach (T item in source) { chunk.Add(item); if (chunk.Count == chunksize) { // force iteration yield return chunk.ToList(); // re-use 'chunk chunk.Clear(); // = new List<T>(chunksize); } } // ToList not needed for final chunk if (chunk.Count != 0) { yield return chunk; }

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