using System;

using System.Collections.Generic;

using System.Linq;

​

public class GroupKey

{

    public string DepartmentName { get; set; }

    //public string PaymentType { get; set; }

    //public DateTime TransactionDate { get; set; }

}

​

public class ReportModel

{

    public string DepartmentName { get; set; }

    public string PaymentType { get; set; }

    public DateTime TransactionDate { get; set; }

    public decimal Amount { get; set; }

}

​

public class Program

{

    public static void Main()

    {

        var data = new List<ReportModel>

        {

            new ReportModel

            {

                DepartmentName = "Dep A",

                PaymentType = "Visa",

                TransactionDate = new DateTime(2024, 9, 3),

                Amount = 100

            },

            new ReportModel

            {

                DepartmentName = "Dep A",

                PaymentType = "Visa",

                TransactionDate = new DateTime(2024, 9, 3),

                Amount = 200

            },

            new ReportModel

            {

                DepartmentName = "Dep A",

                PaymentType = "Master",

                TransactionDate = new DateTime(2024, 9, 3),

                Amount = 300

            },

            new ReportModel

            {

                DepartmentName = "Dep B",

                PaymentType = "Visa",

                TransactionDate = new DateTime(2024, 9, 3),

                Amount = 400

            },

            new ReportModel

            {

                DepartmentName = "Dep B",

                PaymentType = "Mastercard",

                TransactionDate = new DateTime(2024, 9, 3),

                Amount = 500

            }

        };

        var groups = data.GroupBy(model => new GroupKey

        {

            DepartmentName = model.DepartmentName

        }).ToList();

        Console.WriteLine(groups.Count);

    }

}