I was writing a converter that takes a person's date of birth and produces their age in years. I wrote something that looked like this:
public class DateOfBirthToAgeConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var date = value as DateTime?;
if (date == null) return null;
return (DateTime.Now - date).Years;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
I found that there is no Years property on the TimeSpan that results from the subtraction of two DateTime objects. I was somewhat surprised by this. I thought about why there might not be a Years. I figured that it might be because of the leap day, but by that logic, there shouldn't be Days because of daylight savings.
The absence of Months made sense, since there is no standard month length.
I was able to write some different code to get the correct age, but I still really want to know why there is no Years or Weeks property on TimeSpan. Does anyone know the reason?
A TimeSpan only contains the difference between two DateTime values. It is unknown which year this TimeSpan is in. That's also why it doesn't have a Months property.
Example:
TimeSpan.FromDays(60)
How many months are that? 1 or 2?
The absence of Months made sense since there is no standard month length.
There is no standard year length either because of leap years.
Workaround: If you really want to display an approximate value, then doing TimeSpan.TotalDays / 365.2425 will do just fine.
Edit: But only for rough estimations and not for birthdays. In birthday calculation, leap days will accumulate every 4 years as pointed out by Henk Holterman in the comments. Take a look here for calculation of birthdays.
Programmer's life is really hard.
The length of year is variable. Some years have 365 days and some have 366 days. According to the calendar, some years could even have missing days. If talking about culture it becomes more difficult since Chinese lunar calendar can have 13 months a year.
The length of month is variable, and this is well-known. This is also to know that in other calendars things can get worse.
The length of day is variable, because of daylight savings and this is not just culture dependent but also geography dependent.
The length of hour and minute are variable, because of leap seconds.
It seems the only thing that is reliable is the length of a second. So internally, timespan is stored in seconds (or milliseconds, which is the same).
But the variability of time units makes the answer "how many (years/months/days/hours/minites) for n seconds?" being always inaccurate.
This is why the developers end up with a solution that is useful in practical but not precise. They simply ignore daylight savings and leap seconds. However, since people hardly ask about years and months, they just decided not to answer those questions.
Rhetorical question: Without a point of reference, how long is a year?
Because a TimeSpan does not have a fixed point in time, it is not possible to unambiguously say how long a year at an unknown time will be. In the simplest case, it might be 365 or 366 days. There are considerably more cases that would affect the outcome.
I figured that it might be because of the leap day, but by that logic,
there shouldn't be Days because of daylight savings.
You have a point there; subtracting two dates doesn't handle daylight savings ideally. If the dates are local time, you may get an unexpected result.
A change in daylight savings time means a gap or overlap in the local time, and that is ignored if you do calculations with the dates. So, if you want to get the exact difference between two DateTime values that are local time, you should convert them to UTC first as that has linear time:
TimeSpan diff = date1.ToUniversalTime() - date2.ToUniversalTime();
The reason that the TimeSpan doesn't have years is that years differ in length. The daylight savings issue is an effect of how you calculate the TimeSpan and can be circumvented, but there is no "linear years" that you can use to circumvent leap years.
Timespan simply stores number of milliseconds. If you have (1000 * 60 * 60 * 24 * 365.5) 365.5 days worth of milliseconds it's impossible to know if that number of milliseconds spans an entire year and into the next, if it's just short of a year, or if it spans across three years. Same with 30.5 days worth of milliseconds, could span into a second month, could be less than a month, could span across three months.
Assuming you can start with 2 dates and not a single TimeSpan, then you can get the difference in years like this...
The DateTime.AddYears() function has already solved the majority of issues you may encounter with leap years etc. So for a difference in years, start with the earliest of the two dates and repeatedly add 1 year using .AddYears(1) and increment a counter till you have a date which exceeds the later date of the two and the difference in years will be the value of the counter -1.
If you think the 2 dates may be thousands of years apart, you could adapt this logic to repeatedly +100 years, when the later date is exceeded, repeatedly -10 years, when you go below the higher date, finally +1 again till the higher date is exceeded. If you + and - from the counter the number of years you are adding and taking away, you'll end up with counter -1 being the number of whole years difference again.
public int AgeInYears(DateTime date1, DateTime date2)
{
int age = 0;
DateTime low;
DateTime high;
DateTime test;
if(date1 < date2)
{
low = date1;
high = date2;
}
else
{
low = date2;
high = date1;
}
test = low;
while(test < high)
{
test = test.AddYears(100);
age += 100;
}
while (test > high)
{
test = test.AddYears(-10);
age -= 10;
}
while(test <= high)
{
test = test.AddYears(1);
age++;
}
return age - 1;
}
Related
I have a DateTime represented as long (8 bytes), that came from DateTime.ToBinary(), let's call it dateTimeBin. Is there an optimal way of dropping the Time information (I only care for the date) so I can compare it to a start of day? Lets say we have this sample value as a start of day.
DateTime startOfDay = new DateTime(2020,3,4,0,0,0);
long startOfDayBin = startOfDay.ToBinary();
I obviously know I can always convert to a DateTime object then get the date component. However, this operation is going to happen billions of times and every little performance tweak helps.
Is there an efficient way of extracting the Date info of dateTimeBin without converting it to DateTime? Or any arithmetic operation on the long that will return the date only?
Is there a way to match startOfDay (or startOfDayBin) and dateTimeBin if they have the same date components?
Is there a way to see if (dateTimeBin >= startOfDayBin), I don't think the long comparison is valid.
N.B. all the dates are UTC
Since you are working only with UTC dates - makes sense to use DateTime.Ticks instead of DateTime.ToBinary, because former has relatively clear meaning - number of ticks since epoch, just like the unix time, the only difference is unix time interval is second and not tick (where tick is 1/10.000.000 of a second), and epoch is midnight January 1st of 0001 year and not year 1970. While ToBinary only promises that you can restore original DateTime value back and that's it.
With ticks it's easy to extract time and date. To extract time, you need to remainder of division of ticks by number of ticks in a full day, so
long binTicks = myDateTime.Ticks;
long ticksInDay = 24L * 60 * 60 * 10_000_000;
long time = binTicks % ticksInDay;
You can then use convert that to TimeSpan:
var ts = TimeSpan.FromTicks(time);
for convenience, or use as is. The same with extracting only date: just substract time
long date = binTicks - (binTicks % ticksInDay);
Regular comparision (dateTimeBin >= startOfDayBin) in also valid for tick values.
I would like to convert the current time to a decimal representing a fraction of the day. For example, if the day starts at 0, then 12:00 PM should be 0.5.
I need to send that value to an API, and it needs to be in that format. i.e.
"LAST_PRINT_TIME":0.22020833"
Depending on the precision requirements of your result, this may help you:
DateTime now = DateTime.Now;
double dayFraction = (now.Hour + now.Minute / 60d) / 24d;
now.Minute / 60d calculates the fraction of the current hour (so if the time is XX:15 PM this will give 0.25). This is then added to the current hour. This value is then divided by 24 to obtain the final result.
For example, 3:45 PM would go as follows:
(15 + 45 / 60) / 24) => (15 + 0.75) / 24 => 15.75 / 24 => 0.65625
So 3:45 PM, which is 15.75 hours into the day, would be 0.65625 (or 65.625%) of the day.
Or, as #madreflection mentioned in a comment, you could use .ToOADate() as well. In this case, you could do something like:
DateTime now = DateTime.Now;
double dayFraction = now.ToOADate() - now.Date.ToOADate();
This is one of those problems that seems deceptively simple, but the solution is actually much more complex than you would think.
The complexities arise from the nature of local time, whose rules are defined by time zones. Many time zones have transitions that occur either regularly (such as for daylight saving time), or irregularly (such as for changes in standard time).
As such, one needs to consider:
Could the day be shorter or longer than 24 hours?
For example, in most of the US the start of DST is at 2:00 AM, and on that day there are 23 hours in the day because the hour from 2:00 to 2:59 is skipped. At the end of DST, also at 2:00 AM in the US, the hour from 1:00 through 1:59 is repeated, creating 25 hours in that day.
Could the day start or stop at a time other than midnight?
For example, in most of Chile in 2019, the start of DST made the date 2019-09-08 start at 01:00 instead of 00:00.
Learn more in Falsehoods programmers believe about time.
Consider using the following approach to overcome these real-world considerations.
First, define some helper functions to do most of the work. They are not specific to a particular point in time or a particular time zone.
static double GetFractionOfDay(DateTimeOffset dto, TimeZoneInfo tz)
{
// Get the start of the day, and the start of the next day
DateTimeOffset startOfDay = GetStartOfDay(dto, tz);
DateTimeOffset startOfNextDay = GetStartOfDay(startOfDay.AddDays(1), tz);
// Calculate the length of the day. It might not be 24 hours!
TimeSpan lengthOfDay = startOfNextDay - startOfDay;
// Now calculate the position within the day, and the fraction to return
TimeSpan durationSinceStartOfDay = dto - startOfDay;
return durationSinceStartOfDay / lengthOfDay;
}
static DateTimeOffset GetStartOfDay(DateTimeOffset dto, TimeZoneInfo tz)
{
// Make sure we're in the correct time zone
dto = TimeZoneInfo.ConvertTime(dto, tz);
// Start by assuming a local midnight exists
DateTime dt = dto.Date;
// Handle days without a local midnight (these do exist in several time zones)
if (tz.IsInvalidTime(dt))
{
// Advance by the transition gap. This is usually 1 hour, but best not to hard-code that.
TimeSpan[] offsets = { tz.GetUtcOffset(dt.AddDays(-1)), tz.GetUtcOffset(dt.AddDays(1)) };
TimeSpan gap = offsets[1] - offsets[0];
return new DateTimeOffset(dt.Add(gap), offsets[1]);
}
// Handle days with more than one midnight (it's possible, even if unlikely)
if (tz.IsAmbiguousTime(dt))
{
// There's more than one. Prefer the first one, since we want the beginning of the day.
TimeSpan[] offsets = tz.GetAmbiguousTimeOffsets(dt);
TimeSpan offset = offsets[0] > offsets[1] ? offsets[0] : offsets[1];
return new DateTimeOffset(dt, offset);
}
// Clean case, just one local midnight and it does exist
return new DateTimeOffset(dt, tz.GetUtcOffset(dt));
}
With those defined, you can now get an answer to your question with regard to "now" in the local time zone.
double dayFraction = GetFractionOfDay(DateTimeOffset.Now, TimeZoneInfo.Local);
However - Though this is the correct answer of "what fraction of the day is it", keep in mind it may be more important to align with what the receiving API expects, even if not exactly correct. In other words, if 12:00 should always be 0.5, even when it's not exactly at the midpoint of the day, then use elmer007's approach.
This code lets you calulate the difference in months between two dates, Date2 > Date1
public int MonthDiff(DateTime Date1, DateTime Date2)
{
return Math.Abs((Date2.Month - Date1.Month) + 12 * (Date2.Year - Date1.Year));
}
In my example if I put Date1 = "01/01/2019" & Date2 = "31/12/2019", it will return 11, and this is wrong, it should be 12.
Also if I put Date1 = "25/01/2019" & Date = "31/12/2019", it should be 12.
So the question should I need to calculate by Days or what?
I used this code
return Math.Abs(((Date2- Date1).Days / 30) + 12 * (Date2.Year - Date1.Year));
With Date1 = "01/01/2019" & Date2 = "31/12/2020", it shows 36 Months.
If you want to know the difference between two dates in variable length units like months or years, you should use the built in timespan functionality rather than roll your own, and accept some compromises/approximations. The average number of days in a year is 365.2425. The average number of days in a month is 30.42 for a non leap year or 30.50 for a leap year, or 30.44 overall. Choose one of these values when approximating the months. Choose whether to round down, or round up, and to how many decimal places when working out the months/years
For example:
var a = DateTime.Now;
var b = DateTime.Now.AddDays(366);
var years = Math.Round((b-a).TotalDays/365.2425);
You could take some alternative approaches like:
have an array of integers that depict the number of days in each month (over a four year period so leap February are accounted for) and a logic of "I will get the number of days between the two dates, then I will consider the month of the start date and set an array indexer variable pointing to that month in the a"rray-of-month-lengths", and I will subtract the number of days in that month from my total, then I'll move on to the next index in the array (going back to the array start if necessary) and subtract that.. and I'll keep doing it until the remaining total days is lower than the number of days in whatever month I'm looking at.. and the number of times I looped shall be the result of the number of months between the day"
write a loop that adds one day to the start date until the end date is breached, and count how many times the current month number is different to the month number on the last iteration of the loop
etc
These are decisions to implement very specific sorts of approximations
I don't think there is a good fact based answer to your question until you accurately explain every rule you want your math you work to, so all the exceptions can be coded for. Saying "x - y is 11 months and this is wrong" is not a rule; you need to say why it is wrong
Out Time :
2013-03-08 15:00:00.000
In Time :
2013-03-08 11:21:03.290
I need to get Hours and Minutes separately for same date from above, when (Out Time - In Time).
How can I do that ?
I think you probably just want:
TimeSpan difference = outTime - inTime;
int hours = (int) difference.TotalHours;
int minutes = difference.Minutes;
Note that Minutes will give you "just the minutes (never more than 59)" whereas TotalHours (truncated towards zero) will give you "the total number of hours" which might be more than 23 if the times are more than a day apart.
You should also consider what you want to do if the values are negative - either consider it, or explicitly rule it out by validating against it.
The Subtract method on the DateTime class will allow you subtract that date from the other date.
It will give you a TimeSpan which will be the difference.
I'll leave it to you to work out the actual code.
http://msdn.microsoft.com/en-GB/library/8ysw4sby.aspx
You can use Hours property and Minutes
link : http://msdn.microsoft.com/en-us/library/system.datetime.hour.aspx
Requirements:
Calculate the number of months
between two dates: receiveDate and
dueDate.
Both optimistic and pessimistic
calculations are needed
Assumptions:
dueDate will always be the last day of the month.
I've already figured out the pessimistic calculation (meaning a single day overdue counts as a whole month:
if(receiveDate > dueDate)
receiveDate.Month - dueDate.Month + (receiveDate.Year - dueDate.Year) * 12;
Doing a search on the internet turned up several similar examples to confirm this.
Now my instincts tell me the optimistic calculation will just be the same minus one month but for some reason it just doesn't feel right. Am I on the right track or am I missing something?
You're right; if you're looking for the number of complete months between the two dates, subtracting 1 (assuming the receiveDate doesn't fall on the last day of the month, in which case you will have a remainder of 0 days either way) will get you your answer.
If you don't need to keep days of month in your calculus I think it's the way to go.
Your formula calculates the number of months between the first of the receivedDate's month to the first of the dueDate's month. As most time elements in TimeSpan are expressed as TotalXXX, it seems weird that they left out a TotalMonths and a TotalYears.
I think it's because there aren't a fixed number of days from month to month, so it's hard to know what makes most sense in terms of how to express the fractional remainder.
My formula is this...
int nMonthDiff_FirstToFirst = DateTime.Now.Month - testDate.Month + ((DateTime.Now.Year - testDate.Year)* 12);
double dMonthDiff = (double)nMonthDiff_FirstToFirst + (DateTime.Now - testDate.AddMonths(nMonthDiff_FirstToFirst)).TotalDays / (double)DateTime.DaysInMonth(DateTime.Now.Year, DateTime.Now.Month);
So what I'm doing is basically getting the month difference like you are (first of the month to first of the month) then I project my testDate into the future by the month difference. Then with that TimeSpan I get the TotalDays and divide that by the number of days in that month. Thus I'm representing the fractional portion in terms of remaining days of the month.
So if you were going May 5st 2012 -> June 3rd 2012, your formula would return 1 for month difference when a full month hasn't passed yet. In my formula the TotalDays of the projected date would yield a negative fractional number of days, and when added to the 'first to first' month difference, it would take it in as needed.
I am doing this extra check to get precise amount of months:
numberOfMonths = receiveDate.Month - dueDate.Month + (receiveDate.Year - dueDate.Year) * 12;
if (receiveDate.Day > dueDate.Day) numberOfMonths--;
int GetMonthsCount(DateTime dtStart, DateTime dtEnd)
{
return (int)Math.Round((dtEnd - dtStart).TotalMonths);
}