using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class Product

    {

        public string Group { get; set; }

        public (string Item1, string Item2)[] ValeursAndUids { get; set; }

    }

    public static void Main()

    {

        var idA = "QB32-20220325-486274";

        var idB = "QB32-20220325-106045";

        var idC = "QB32-20220325-205994";

        var idD = "QB32-20220325-270903";

​

        Product product1 = new()

        {

            Group = "coloris",

            ValeursAndUids = new[]

            {

                ( "Beige", idA ),

                ( "Beige", idB ),

                ( "Venezia", idC ),

                ( "Venezia", idD )

            }

        };

​

        Product product2 = new()

        {

            Group = "ref_commercial",

            ValeursAndUids = new[]

            {

                ( "29245", idA ),

                ( "29245", idB ),

                ( "29245", idC ),

                ( "29245", idD )

            }

        };

​

        Product product3 = new()

        {

            Group = "Address",

            ValeursAndUids = new[]

            {

                ( "172 B", idA ),

                ( "172 B", idB ),

                ( "1725 A", idC ),

                ( "1725 A", idD )

            }

        };

​

        Product[] products = new[] { product1, product2, product3 };

​

        List<((string GroupName, string Valeur)[] Levels, string[] Uids)> groupings = products

            // Step 1:

            .SelectMany(p => p.ValeursAndUids

                .Select(vu => ( GroupName: p.Group, Valeur: vu.Item1, Uid: vu.Item2)))

            // Step 2:

            .GroupBy(item => item.Uid,

                item => ( item.GroupName, item.Valeur) )

            // Step 3:

            .GroupBy(itemsByUid => string.Join(string.Empty, itemsByUid.Select(_ => _)),

                 // Step 4:

                 (_, nestedGroup) => (

                     Levels: nestedGroup.First().Select(level => level).ToArray(),

                     Uids: nestedGroup.Select(itemsByUid => itemsByUid.Key).ToArray()

                 ))

            .ToList();

        // Level-wise printing

        const string tab = "\t";

        string tabs;

​

        foreach (var grouping in groupings)

        {

            tabs = string.Empty;

​

            foreach (var level in grouping.Levels)

            {

                Console.WriteLine($"{tabs}{level.GroupName} {level.Valeur}");

​

                tabs += tab;

            }

​

            foreach (var uid in grouping.Uids)

            {

                Console.WriteLine($"{tabs}{uid}");

            }

        }

    }

}