/// <summary>
        /// Показать расходы по категориям.
        /// </summary>
        /// <param name="category"> Категория расхода. </param>
        public void ShowActionsByCategory(string category)
        {
            List <Spending> spendingsByCategory = Spendings.FindAll(s => s.Category == category);
            List <Income>   incomesByCategory   = Incomes.FindAll(i => i.Category == category);

            if (spendingsByCategory.Count != 0)
            {
                spendingsByCategory.Sort((s1, s2) => DateTime.Compare(s1.DateAdded, s2.DateAdded));
                spendingsByCategory.ForEach(s => Console.WriteLine(s));
                Console.WriteLine();
            }
            else if (incomesByCategory.Count != 0)
            {
                incomesByCategory.Sort((s1, s2) => DateTime.Compare(s1.DateAdded, s2.DateAdded));
                incomesByCategory.ForEach(s => Console.WriteLine(s));
                Console.WriteLine();
            }
            else
            {
                Console.WriteLine("Категория пуста.");
            }
        }