protected override object BuildGroupKey(DateTime time)
        {
            var dateKey = new ChartItemDateKey
            {
                Year  = time.Year,
                Month = time.Month
            };

            return(dateKey);
        }
 protected abstract DateTime GetDateTimeFromGroupKey(ChartItemDateKey groupKey);
        protected override DateTime GetDateTimeFromGroupKey(ChartItemDateKey dateKey)
        {
            var dateTime = new DateTime(dateKey.Year, dateKey.Month, dateKey.Day);

            return(dateTime);
        }