ChunkExtensions.cs

namespace CapitalSix.Linq.Extensions
{
    public static class ChunkExtensions
    {
        public const int DEFAULT_CHUNK_SIZE = 2000;

        /// <summary>
        /// Process a list of T in chunks of size {chunkSize}
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="all">The original list of items</param>
        /// <param name="chunkAction">Action to perform on each chunk</param>
        /// <param name="chunkSize">Size of each chunk</param>
        /// <returns>The original list of items</returns>
        public static IEnumerable<T> Chunked<T>(this IEnumerable<T> all, Action<IEnumerable<T>> chunkAction, int chunkSize = DEFAULT_CHUNK_SIZE)
        {
            IEnumerable<IEnumerable<T>> chunks = all.Chunks(chunkSize);

            foreach (IEnumerable<T> chunk in chunks)
            {
                chunkAction(chunk);
            }
            return all;
        }

        /// <summary>
        /// Split an enumerable set into chunks of size {chunkSize}
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="all">The original list of items</param>
        /// <param name="chunkSize">Size of each chunk</param>
        /// <returns>A list of chunks</returns>
        public static IEnumerable<IEnumerable<T>> Chunks<T>(this IEnumerable<T> all, int chunkSize = DEFAULT_CHUNK_SIZE)
            => all
                .Select((item, index) => (Item: item, Index: index))
                .GroupBy(chunkItem => chunkItem.Index / chunkSize)
                .Select(chunkItem => chunkItem.Select(x => x.Item).ToList());
    }

}