using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var transactions = new List<Transaction>

            {

                new Transaction { Category = "Saving Account", Amount = 56, Date = DateTime.Today.AddDays(1) },

                new Transaction { Category = "Saving Account", Amount = 10, Date = DateTime.Today.AddDays(-10) },

                new Transaction { Category = "Credit Card", Amount = 15, Date = DateTime.Today.AddDays(1) },

                new Transaction { Category = "Credit Card", Amount = 56, Date = DateTime.Today },

                new Transaction { Category = "Current Account", Amount = 100, Date = DateTime.Today.AddDays(5) },

            };

​

​

        var summaryApproach1 = transactions.GroupBy(t => t.Category)

                           .Select(t => new

                           {

                               Category = t.Key,

                               Count = t.Count(),

                               Amount = t.Sum(ta => ta.Amount),

                           }).ToList();

​

        Console.WriteLine("-- Summary: Approach 1 --");

        summaryApproach1.ForEach(

            row => Console.WriteLine($"Category: {row.Category}, Amount: {row.Amount}, Count: {row.Count}"));

​

​

​

        var summaryApproach2 = transactions.GroupBy(t => t.Category, (key, t) =>

        {

            var transactionArray = t as Transaction[] ?? t.ToArray();

            return new

            {

                Category = key,

                Count = transactionArray.Length,

                Amount = transactionArray.Sum(ta => ta.Amount),

            };

        }).ToList();

​

        Console.WriteLine("-- Summary: Approach 2 --");

        summaryApproach2.ForEach(

            row => Console.WriteLine($"Category: {row.Category}, Amount: {row.Amount}, Count: {row.Count}"));

    }

}

​

public class Transaction

{

    public string Category { get; set; }

    public DateTime Date { get; set; }

    public decimal Amount { get; set; }

}

​

​