Given two datetimes. What is the best way to calculate the number of working hours between them. Considering the working hours are Mon 8 - 5.30, and Tue-Fri 8.30 - 5.30, and that potentially any day could be a public holiday.
This is my effort, seem hideously inefficient but in terms of the number of iterations and that the IsWorkingDay method hits the DB to see if that datetime is a public holiday.
Can anyone suggest any optimizations or alternatives.
public decimal ElapsedWorkingHours(DateTime start, DateTime finish)
{
decimal counter = 0;
while (start.CompareTo(finish) <= 0)
{
if (IsWorkingDay(start) && IsOfficeHours(start))
{
start = start.AddMinutes(1);
counter++;
}
else
{
start = start.AddMinutes(1);
}
}
decimal hours;
if (counter != 0)
{
hours = counter/60;
}
return hours;
}
Before you start optimizing it, ask yourself two questions.
a) Does it work?
b) Is it too slow?
Only if the answer to both question is "yes" are you ready to start optimizing.
Apart from that
you only need to worry about minutes and hours on the start day and end day. Intervening days will obviously be a full 9/9.5 hours, unless they are holidays or weekends
No need to check a weekend day to see if it's a holiday
Here's how I'd do it
// Normalise start and end
while start.day is weekend or holiday, start.day++, start.time = 0.00am
if start.day is monday,
start.time = max(start.time, 8am)
else
start.time = max(start.time, 8.30am)
while end.day is weekend or holiday, end.day--, end.time = 11.59pm
end.time = min(end.time, 5.30pm)
// Now we've normalised, is there any time left?
if start > end
return 0
// Calculate time in first day
timediff = 5.30pm - start.time
day = start.day + 1
// Add time on all intervening days
while(day < end.day)
// returns 9 or 9.30hrs or 0 as appropriate, could be optimised to grab all records
// from the database in 1 or 2 hits, by counting all intervening mondays, and all
// intervening tue-fris (non-holidays)
timediff += duration(day)
// Add time on last day
timediff += end.time - 08.30am
if end.day is Monday then
timediff += end.time - 08.00am
else
timediff += end.time - 08.30am
return timediff
You could do something like
SELECT COUNT(DAY) FROM HOLIDAY WHERE HOLIDAY BETWEEN #Start AND #End GROUP BY DAY
to count the number of holidays falling on Monday, Tuesday, Wednesday, and so forth. Probably a way of getting SQL to count just Mondays and non-Mondays, though can't think of anything at the moment.
especially considering the IsWorkingDay method hits the DB to see if that day is a public holiday
If the problem is the number of queries rather than the amount of data, query the working day data from the data base for the entire day range you need at the beginning instead of querying in each loop iteration.
There's also the recursive solution. Not necessarily efficient, but a lot of fun:
public decimal ElapseddWorkingHours(DateTime start, DateTime finish)
{
if (start.Date == finish.Date)
return (finish - start).TotalHours;
if (IsWorkingDay(start.Date))
return ElapsedWorkingHours(start, new DateTime(start.Year, start.Month, start.Day, 17, 30, 0))
+ ElapsedWorkingHours(start.Date.AddDays(1).AddHours(DateStartTime(start.Date.AddDays(1)), finish);
else
return ElapsedWorkingHours(start.Date.AddDays(1), finish);
}
Take a look at the TimeSpan Class. That will give you the hours between any 2 times.
A single DB call can also get the holidays between your two times; something along the lines of:
SELECT COUNT(*) FROM HOLIDAY WHERE HOLIDAY BETWEEN #Start AND #End
Multiply that count by 8 and subtract it from your total hours.
-Ian
EDIT: In response to below, If you're holiday's are not a constant number of hours. you can keep a HolidayStart and a HolidayEnd Time in your DB and and just return them from the call to the db as well. Do an hour count similar to whatever method you settle on for the main routine.
Building on what #OregonGhost said, rather than using an IsWorkingDay() function at accepts a day and returns a boolean, have a HolidayCount() function that accepts a range and returns an integer giving the number of Holidays in the range. The trick here is if you're dealing with a partial date for your boundry beginning and end days you may still need to determine if those dates are themselves holidays. But even then, you could use the new method to make sure you needed at most three calls the to DB.
Try something along these lines:
TimeSpan = TimeSpan Between Date1 And Date2
cntDays = TimeSpan.Days
cntNumberMondays = Iterate Between Date1 And Date2 Counting Mondays
cntdays = cntdays - cntnumbermondays
NumHolidays = DBCall To Get # Holidays BETWEEN Date1 AND Date2
Cntdays = cntdays - numholidays
numberhours = ((decimal)cntdays * NumberHoursInWorkingDay )+((decimal)cntNumberMondays * NumberHoursInMondayWorkDay )
Use #Ian's query to check between dates to find out which days are not working days. Then do some math to find out if your start time or end time falls on a non-working day and subtract the difference.
So if start is Saturday noon, and end is Monday noon, the query should give you back 2 days, from which you calculate 48 hours (2 x 24). If your query on IsWorkingDay(start) returns false, subtract from 24 the time from start to midnight, which would give you 12 hours, or 36 hours total non-working hours.
Now, if your office hours are the same for every day, you do a similar thing. If your office hours are a bit scattered, you'll have more trouble.
Ideally, make a single query on the database that gives you all of the office hours between the two times (or even dates). Then do the math locally from that set.
The most efficient way to do this is to calculate the total time difference, then subtract the time that is a weekend or holiday. There are quite a few edge cases to consider, but you can simplify that by taking the first and last days of the range and calculating them seperately.
The COUNT(*) method suggested by Ian Jacobs seems like a good way to count the holidays. Whatever you use, it will just handle the whole days, you need to cover the start and end dates separately.
Counting the weekend days is easy; if you have a function Weekday(date) that returns 0 for Monday through 6 for Sunday, it looks like this:
saturdays = ((finish - start) + Weekday(start) + 2) / 7;
sundays = ((finish - start) + Weekday(start) + 1) / 7;
Note: (finish - start) isn't to be taken literally, replace it with something that calculates the time span in days.
Dim totalMinutes As Integer = 0
For minute As Integer = 0 To DateDiff(DateInterval.Minute, contextInParameter1, contextInParameter2)
Dim d As Date = contextInParameter1.AddMinutes(minute)
If d.DayOfWeek <= DayOfWeek.Friday AndAlso _
d.DayOfWeek >= DayOfWeek.Monday AndAlso _
d.Hour >= 8 AndAlso _
d.Hour <= 17 Then
totalMinutes += 1
Else
Dim test = ""
End If
Next minute
Dim totalHours = totalMinutes / 60
Piece of Cake!
Cheers!
Related
Let's say I have 21875 as totalQuantityNumber.
I need to split the totalQuantityNumber on multiple days in a for loop ex. first day 20000 and the second day 1875.
Inside my for loop at the end I do a sum of the splitted quantity so I can verify later if the splitting is correct ex. totalSplittedQuantity += splittedQuantity.
At the end of my splitting I verify if the total sum of my splitted products number is the same with the initial planned total products number ex. totalQuantityNumber== totalSplittedQuantity which it should be 21875 == 21875 but I am always off by one number when the number is odd ex. 21875 == 21874. I tried to make the division decimal and round it up at the end but the problem still persists and some of the times the result is over by one as well ex. 21875 == 21876.
This is my division inside the loop:
splittedQuantity = splittedDiffDuration * totalQuantityNumber/ totalDuration;
totalDuration and splittedDiffDuration are in minutes ex. totalDuration = 120; splittedDiffDuration = 60;
Basically I loop through each day from a DateTime interval (startDate, endDate) ex. Monday to Tuesday - splitting the quantity for each day for the duration they were planned ex. let's say on Monday its planned 60 minutes to produce X quantity and on Tuesday the same, 60 minutes to produce the rest of the quantity.
I am new to programming and not so good at math. What am I doing wrong with my division?
Regardless of numbers type (integer, decimal, floating point) there will be an error due to rounding or number representation.
To achieve what you want, you need to calculate the last proportion as the difference between total and the sum of all previous proportions.
E.g., given this total and this percentage:
Total: 100
Day 1: 30%
Day 2: 17&
Day 3: 53%
proportions will be:
Day 1: 100 * 30% = 30
Day 2: 100 * 17% = 17
Day 3: Total - (Day1 + Day2) = 100 - (30 + 17) = 53.
This, of course, gives you approximate result for the last one, but it's the only way to get this expression to be always true:
(Day 1 + Day2 + Day3) = Total
This question already has answers here:
Timer callback raised every 24 hours - is DST handled correctly?
(3 answers)
Closed 5 years ago.
I'm not in front of my code right now, but don't really think I need it to ask this question. So I have a countdown timer that goes off every 18 hours and then resets. The timer checks the current DateTime.Now and adjusts the countdown timer as needed. I am having an issue trying to account for when daylight savings when it goes back an hour because; for example this past event on November 5th 2017 at 2am it goes back to 1am but when I do DateTime.IsDaylightSavingTime() it tells me that it's false even though Daylight Saving Time just went off. This makes my timer go back an extra hour because it thinks that Daylight Saving Time still hasn't happen for that one hour period. How would I get around this?
If you realy need to use local time for some reason, than you should count for DST changes in advance (prior scheduling next event).
TimeZoneInfo.GetAdjustmentRules() should help you to get the time and delta of next DST adjustment.
Following is the code for getting upcomming adjustment:
public static DateTime? GetNextAdjustmentDate(TimeZoneInfo timeZoneInfo)
{
var adjustments = timeZoneInfo.GetAdjustmentRules();
if (adjustments.Length == 0)
{
return null;
}
int year = DateTime.UtcNow.Year;
TimeZoneInfo.AdjustmentRule adjustment = null;
foreach (TimeZoneInfo.AdjustmentRule adjustment1 in adjustments)
{
// Determine if this adjustment rule covers year desired
if (adjustment1.DateStart.Year <= year && adjustment1.DateEnd.Year >= year)
adjustment = adjustment1;
}
if (adjustment == null)
return null;
//TimeZoneInfo.TransitionTime startTransition, endTransition;
DateTime dstStart = GetCurrentYearAdjustmentDate(adjustment.DaylightTransitionStart);
DateTime dstEnd = GetCurrentYearAdjustmentDate(adjustment.DaylightTransitionEnd);
if (dstStart >= DateTime.UtcNow.Date)
return dstStart;
if (dstEnd >= DateTime.UtcNow.Date)
return dstEnd;
return null;
}
private static DateTime GetCurrentYearAdjustmentDate(TimeZoneInfo.TransitionTime transitionTime)
{
int year = DateTime.UtcNow.Year;
if (transitionTime.IsFixedDateRule)
return new DateTime(year, transitionTime.Month, transitionTime.Day);
else
{
// For non-fixed date rules, get local calendar
System.Globalization.Calendar cal = CultureInfo.CurrentCulture.Calendar;
// Get first day of week for transition
// For example, the 3rd week starts no earlier than the 15th of the month
int startOfWeek = transitionTime.Week * 7 - 6;
// What day of the week does the month start on?
int firstDayOfWeek = (int)cal.GetDayOfWeek(new DateTime(year, transitionTime.Month, 1));
// Determine how much start date has to be adjusted
int transitionDay;
int changeDayOfWeek = (int)transitionTime.DayOfWeek;
if (firstDayOfWeek <= changeDayOfWeek)
transitionDay = startOfWeek + (changeDayOfWeek - firstDayOfWeek);
else
transitionDay = startOfWeek + (7 - firstDayOfWeek + changeDayOfWeek);
// Adjust for months with no fifth week
if (transitionDay > cal.GetDaysInMonth(year, transitionTime.Month))
transitionDay -= 7;
return new DateTime(year, transitionTime.Month, transitionDay);
}
}
You'd need to add some more code to retrieve and apply the adjustment delta.
Well - now, when you see all the hard work that would need to be done (and than maintained and made sure to be bug free), you might want to rething your problem to be able to use UTC.
I would use DateTime.UtcNow you won't have the issue with daylight savings
I feel like this is something really simple, but my Google Fu is letting me down as I keep finding difference calculations.
I have a time (e.g. 1800 hours) stored in a DateTime object. The date is null and immaterial. All I want to know is how many milliseconds until the NEXT occurrence of that time.
So, if I run the calculation at 0600 - it will return 12 hours (in ms). At 1750, it will return ten minutes (in ms) and at 1900 it will return 24 hours (in ms).
All the things I can find show me how to calculate differences, which doesn't work once you're past the time.
Here is what I tried, but fails once you're past the time and gives negative values:
DateTime nowTime = DateTime.Now;
TimeSpan difference = _shutdownTime.TimeOfDay - nowTime.TimeOfDay;
double result = difference.TotalMilliseconds;
You're already doing everything you should, except for one thing: handling negative results.
If the result is negative, it means the time you want to calculate the duration until has already passed, and then you want it to mean "tomorrow" instead, and get a positive value.
In this case, simply add 24 hours:
DateTime nowTime = DateTime.Now;
TimeSpan difference = _shutdownTime.TimeOfDay - nowTime.TimeOfDay;
double result = difference.TotalMilliseconds;
if (result < 0)
result += TimeSpan.FromHours(24).TotalMilliseconds;
The next thing to consider is this: If the time you want to calculate the duration until is 19:00 hours, and the current time is exactly 19:00 hours, do you want it to return 0 (zero) or 24 hours worth of time? Meaning, do you really want the next such occurrence?
If so, then change the above if-statement to use <=:
DateTime nowTime = DateTime.Now;
TimeSpan difference = _shutdownTime.TimeOfDay - nowTime.TimeOfDay;
double result = difference.TotalMilliseconds;
if (result <= 0)
result += TimeSpan.FromHours(24).TotalMilliseconds;
However, note that this will be prone to the usual problems with floating point values. If the current time is 18:59:59.9999999, do you still want it to return the current time (a minuscule portion of time) until 19:00 today, or do you want it to flip to tomorrow? If so, change the comparison to be slightly different:
DateTime nowTime = DateTime.Now;
TimeSpan difference = _shutdownTime.TimeOfDay - nowTime.TimeOfDay;
double result = difference.TotalMilliseconds;
if (result <= -0.0001)
result += TimeSpan.FromHours(24).TotalMilliseconds;
where -0.0001 is a value that corresponds to "the range of inaccuracy you're prepared to accept being tomorrow instead of today in terms of milliseconds".
When doing calculations like this it is important to take possible DST changes under consideration so that your results remain correct.
Suppose your operational parameters are:
var shutdownTime = TimeSpan.FromHours(18);
// just to illustrate, in Europe there is a DST change on 2013-10-27
// normally you 'd just use DateTime.Now here
var now = new DateTime(2013, 10, 26, 20, 00, 00);
// do your calculations in local time
var nextShutdown = now.Date + shutdownTime;
if (nextShutdown < now) {
nextShutdown = nextShutdown.AddDays(1);
}
// when you want to calculate time spans in absolute time
// (vs. wall clock time) always convert to UTC first
var remaining = nextShutdown.ToUniversalTime() - now.ToUniversalTime();
Console.WriteLine(remaining);
The answer to your question would now be remaining.TotalMilliseconds.
long ticks = new DateTime(2012, 1, 31).ToLocalTime().Ticks; // 634635684000000000
But how to do this without DateTime constructor ?
edit
What I actually want is to keep only the years, months and days from the ticks.
long ALL_Ticks = DateTime.Now.Ticks; // 634636033446495283
long Only_YearMonthDay = 634635684000000000; // how to do this ?
I want to use this in a linq-sql query using Linq.Translations.
If you only want the ticks for the date portion of the current datetime you could use:
long Only_YearMonthDay = DateTime.Now.Date.Ticks; //634635648000000000
//DateTime.Now.Date.Ticks + DateTime.Now.TimeOfDay.Ticks == DateTime.Now.Ticks
You could find out how many days are in the calculation and then multiply by 864,000,000,000 (which is how many ticks are in a day). Is that what you are looking for? Bit of documentation here : http://msdn.microsoft.com/en-us/library/system.timespan.ticksperday.aspx.
Happy coding,
Cheers,
Chris.
OK - didn't think this through properly! Ticks represent the amount of 100 nanosecond intervals since 12:00:00 midnight, January 1, 0001. You would need to calculate how many days have passed since that date and then multiply it by the ticks per day value!
If I understand you right, you are not worried about the ticks up to a particular time of the day?! So, it would be something along the lines of :
var ticksToDate = (DateTime.UtcNow - DateTime.MinValue).Days * 864000000000;
Does that answer your question??
That is going to be rather difficult unless you have some other way of getting the current date and time. According to MSDN:
A single tick represents one hundred nanoseconds or one ten-millionth of a second. There are 10,000 ticks in a millisecond.
The value of this property represents the number of 100-nanosecond intervals that have elapsed since 12:00:00 midnight, January 1, 0001, which represents DateTime.MinValue. It does not include the number of ticks that are attributable to leap seconds.
Now, if you know the current date and time, you can calculate how many days have passed since January 1, 0001 and use that to calculate the number of ticks.
I understand you dont want the hour parts of the date. If you use Date, then you only get the day (for example: 01/01/2012 00:00:00)
long ticks = new DateTime(2012, 1, 31).Date.Ticks;
And with any DateTime object already created is the same of course.
long ticks = dateObject.Date.Ticks;
You already have the answer there in your post:
long ALL_Ticks = DateTime.Now.Ticks;
// that's the ticks (from DateTime.MinValue) until 'now' (this very moment)
long ticks = new DateTime(2012, 1, 31).ToLocalTime().Ticks;
// or
long ticks = DateTime.Now.Date.Ticks;
// that's the ticks until the beginning of today
long yearmonthticks = new DateTime(2012, 1, 1).ToLocalTime().Ticks;
// that's the ticks until the beginning of the month
// etc..., the rest is simple subtractions
Since your question doesn't specify any reason not to use the DateTime constructor, this is the best solution for what seems like your problem.
I had a use case where I couldn't use DateTime but needed Years/Months from Ticks.
I used the source behind DateTime to figure out how. To go the other way you can look at the constructor, one of which calls the following code.
private static long DateToTicks(int year, int month, int day) {
if (year >= 1 && year <= 9999 && month >= 1 && month <= 12) {
int[] days = IsLeapYear(year)? DaysToMonth366: DaysToMonth365;
if (day >= 1 && day <= days[month] - days[month - 1]) {
int y = year - 1;
int n = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
return n * TicksPerDay;
}
}
throw new ArgumentOutOfRangeException(null, Environment.GetResourceString("ArgumentOutOfRange_BadYearMonthDay"));
}
This can be found in link below, of course you will need to re-write to suit your needs and look up the constants and IsLeapYear function too.
https://referencesource.microsoft.com/#mscorlib/system/datetime.cs,602
The language I am using is C#.
I have the folowing dillema.
DateTime A, DateTime B. If A < B then I have to calculate the number of days per year in that timespan and multiply it by a coeficient that corresponds to that year.
My problem is the fact that it can span multiple years.
For example:
Nr of Days in TimeSpan for 2009 * coef for 2009 + Nr of Days in TimeSpan for 2010 * coef for 2010 + etc
You can't do this with a simple TimeSpan, basically. It doesn't know anything about when the span covers - it's just a number of ticks, really.
It sounds to me like there are two cases you need to consider:
A and B are in the same year. This is easy - just subtract one from the other and get the number of days from that
A and B are in different years. There are now either two or three cases:
The number of days after A in A's year. You can work this out by constructing January 1st in the following year, then subtracting A
The number of days in each year completely between A and B (so if A is in 2008 and B is in 2011, this would be 2009 and 2010)
The number of days in B's year. You can work this out by constructing December 31st in the previous year, then subtracting B. (Or possibly January 1st in B's year, depending on whether you want to count the day B is on or not.)
You can use DateTime.IsLeapYear to determine whether any particular year has 365 or 366 days in it. (I assume you're only using a Gregorian calendar, btw. All of this changes if not!)
Here is a little snippet of code that might help
var start = new DateTime(2009, 10, 12);
var end = new DateTime(2014, 12, 25);
var s = from j in Enumerable.Range(start.Year, end.Year + 1 - start.Year)
let _start = start.Year == j ? start : new DateTime(j, 1, 1)
let _end = end.Year == j ? end : new DateTime(j, 12, 31)
select new {
year = j,
days = Convert.ToInt32((_end - _start).TotalDays) + 1
};
If I understood your problem correctly, solving it using Inclusion Exclusion principle would be the best.
Say, if your start date is somewhere in 2008 and the end date is in 2010:
NDAYS(start, end) * coeff_2008
- NDAYS(2009, end) * coeff_2008 + NDAYS(2009, end) * coeff_2009
- NDAYS(2010, end) * coeff_2009 + NDAYS(2010, end) * coeff_2010
Where Ndays computes the number of dates in the interval (TotalDays plus one day).
There is no need to handle leap years specially or compute december 31st.
The details you can work out in a for-loop going over jan first of each year in the span.