How to write a method that loops through a given interval by hour

[MrNorth]

Hi!

Our customer has a data model where the data is represented by date and hour. Dates are normal dates like "2014-01-01" and there is a separate property on the model for the Hour, from 1 to 24.

How should I write a simple method that accepts startdate, starthour, enddate, endhour and loop through each hour?

I tried using this code:

 public List<DateTime> GetAllHoursInInterval(DateTime startDate, int startHour, DateTime endDate,
            int endHour)
        {
            var dates = new List<DateTime>();
          
            for (var date = startDate.AddHours(startHour); date <= endDate.AddHours(endHour); date = date.AddHours(1))
            {
                Debug.WriteLine("Date: " + date.ToShortDateString());
                Debug.WriteLine("Hour: " + (date.Hour));
                dates.Add(date);
            }
            return dates;
        }

But there is a mismatch in the datetime hours and the hours in the data model, since the datetime likes to start from hour 0 to 23.

I want to work with the model hour, but in the loop I guess I should stick with the DateTime hours...

Preferrably this method should handle daylight savings and stuff...

/H

[dolot]

Have you tried using starthour -1 and endhour -1 - to get your base 1 system lined up with the base 0 system of the datetime object?

Just a guess.

[MrNorth]

Hi!

Sorry for c#, apparently I didn't have vb installed on this client.

I solved it by not returning DateTimes, since they are a somewhat different animal than what they have in the model. I created a simple model class representing the date and hours wiht two properties, one datetime for the date, and one integer for the hours (1-24)

I then used the standard datetime functionality like this:

public List<DateTimeValue> GetAllHoursInInterval(DateTime startDate, int startHour, DateTime endDate,
            int endHour)
        {
            var dates = new List<DateTimeValue>();
          
            for (var date = startDate.AddHours(startHour); date <= endDate.AddHours(endHour); date = date.AddHours(1))
            {
                Debug.WriteLine("Date: " + date.ToShortDateString());
                Debug.WriteLine("Hour: " + (date.Hour));
                dates.Add(new DateTimeValue{Date = date, Hour = date.Hour == 0 ? 24 : date.Hour});
            }
            return dates;
        }

Since the Hour property is only -23 to 23 I had to add a "twist" to the loop to get the last 24th hour.

I have written a few unit tests to validate the functionality and it seems to check out ok. And hopefully the codesmell is not so bad...

I guess the whole thing could be solved with a few nested for loops and if statements as well...

/S

[MrNorth]

Well, the above code was faulty... so I gave up trying to use DateTime objects for the enumeration, and resorted to a nested for loop.

 public List<DateTimeValue> GetListOfDatesByHour(DateTime startDate, DateTime stopDate, int startHour, int stopHour)
        {
            var noOfDays = (stopDate - startDate).Days + 1; 
            var dateTimes = new List<DateTimeValue>();

            for(int days = 0; days < noOfDays; days ++)
            {
                // Handles if it is the first, middle or last day.
                var localStartHour = days == 0 ? startHour : 1;
                var localStopHour = days == noOfDays - 1 ? stopHour : 24;

                for (int hour = localStartHour; hour <= localStopHour; hour++)
                {
                    dateTimes.Add(new DateTimeValue
                    { 
                        Date = startDate.AddDays(days), 
                        Hour = hour
                    });

                    // Go to next day.
                    if (hour == 24) continue;                    
                }
            }
            return dateTimes.OrderBy(x => x.Date).ThenBy(x => x.Hour).ToList();
        }

The above code seems to work better, but I would love if you guys could take a look at it, and suggest further refactorings, some things bother me:

* Are the ? expressions really needed, or can this be handled in a more clever way?

* The OrderBy, it shouldn't be needed, given the code, but can I be 100 % sure?

* I know I miss some guard clauses for invalid input parameters...


/H

[dday9]

Moved to C#.