using System;

using System.Collections.Generic;

using System.Linq;

​

public class ProjectResult

{

    public string Month { get; set; }

    public string Name { get; set; }

    // Other properties

}

​

public class DynamicProjectCalendarAug

{

    public int GroupRowId { get; set; }

    public string MonthYear { get; set; }

    public string ProjectName { get; set; }

    // Other properties

    public override string ToString() => $"{GroupRowId}  |  {MonthYear}  |  {ProjectName}";

}

​

public class Program

{

    public static void Main()

    {

        List<ProjectResult> result = new()

        {

            new() { Month = "2020-08", Name = "Project 1"},

            new() { Month = "2020-08", Name = "Project 2"},

            new() { Month = "2020-08", Name = "Project 3"},

            new() { Month = "2021-08", Name = "Project 4"},

            new() { Month = "2021-08", Name = "Project 5"},

            new() { Month = "2021-08", Name = "Project 6"}

        };

        var queryAug = result

            //.Where( ... )

            .GroupBy(resultItem => resultItem.Month,

                ( _, itemsInMonth ) => itemsInMonth

                     .Select(( item, i ) => new DynamicProjectCalendarAug {

                         GroupRowId = i + 1,

                         MonthYear = item.Month,

                         ProjectName = item.Name,

                         //Aug = ...

                     }))

            .SelectMany(_ => _)

            .ToList();

        Console.WriteLine(string.Join(Environment.NewLine, queryAug));

    }

}