public void CalculateResults()
{
Years.Clear();
var expenses = _expenseRepository.Load();
var expensesPerYear = expenses.GroupBy(e => e.Date.Year);
var yearPresentations = expensesPerYear
.Select(yearExpense => new YearResultsPresentation(yearExpense.Key, yearExpense.ToArray(), _categorizer));
Years.AddRange(yearPresentations);
}