using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

public class Order

{

    [JsonProperty("Order Number")]

    public string OrderNumber { get; set; }

    [JsonProperty("Order Date")]

    public string OrderDate { get; set; }

    [JsonProperty("SKU")]

    public string SKU { get; set; }

    [JsonProperty("Quantity")]

    public string Quantity { get; set; }

}

​

public class OrderBase

{

    public OrderItem Order { get; set; }

}

public class OrderItem

{

    public string OrderNumber { get; set; }

    public string TotalUnits { get; set; }

    public IEnumerable<OrderLine> OrderLines { get; set; }

}

public class OrderLine

{

    public string OrderedQty { get; set; }

    public string Product { get; set; }

}

​

public class Program

{

​

    public static void Main(string[] args)

    {

        string input = @"[{""Order Number"":""10188"",""Order Date"":""05/06/2021"",""SKU"":""LW80S"",""Quantity"":""3""},{""Order Number"":""10187"",""Order Date"":""05/06/2021"",""SKU"":""LW90L"",""Quantity"":""1""},{""Order Number"":""10187"",""Order Date"":""05/06/2021"",""SKU"":""LW80S"",""Quantity"":""1""},{""Order Number"":""10187"",""Order Date"":""05/06/2021"",""SKU"":""CCDW12"",""Quantity"":""1""},{""Order Number"":""10187"",""Order Date"":""05/06/2021"",""SKU"":""CSS"",""Quantity"":""1""}]";

        List<Order> orders = JsonConvert.DeserializeObject<List<Order>>(input);

        Dictionary<string, List<OrderLine>> lookup = new Dictionary<string, List<OrderLine>>();

        // Group into lookup

        foreach (Order item in orders)

        {

            OrderLine newItem = new OrderLine

            {

                Product = item.OrderNumber,

                OrderedQty = item.Quantity

            };

            if (!lookup.ContainsKey(item.OrderNumber))

            {

                lookup[item.OrderNumber] = new List<OrderLine> { newItem };

            }

            else

            {

                lookup[item.OrderNumber].Add(newItem);

            }

        }

        List<OrderBase> results = new List<OrderBase>();

        foreach (var kvp in lookup)

        {

            results.Add(

                new OrderBase

                {

                    Order = new OrderItem

                    {

                        OrderNumber = kvp.Key,

                        TotalUnits = kvp.Value.Count.ToString(),

                        OrderLines = kvp.Value

                    }

                }

            );

        }

        Console.WriteLine("Response - {0}", JsonConvert.SerializeObject(results, Formatting.Indented));

    }

}