public Dictionary<IGtpKey, List<IVoltageGraphParameterValue>> Select(
            IEnumerable<IGtpKey> gtps,
            LocalDate? operationDay = null)
        {
            if (gtps == null)
            {
                throw new ArgumentNullException("gtps");
            }

            LocalDate operationDayValue = operationDay ?? CalendarDateContext.CurrentDate;

            Dictionary<IGtpKey, List<IVoltageGraphParameterValue>> result = gtps.ToDictionary(
                x => x,
                x => new List<IVoltageGraphParameterValue>());

            foreach (IVoltageGraphParameterValue voltageGraphParameterValue in AtOperationDay(operationDayValue))
            {
                List<IVoltageGraphParameterValue> deviceParameterValues;
                if (result.TryGetValue(voltageGraphParameterValue.Gtp, out deviceParameterValues))
                {
                    deviceParameterValues.Add(voltageGraphParameterValue);
                }
            }

            return result;
        }