I am trying to find the duration between two times with the below code:
DateTimeFormatter formatter = DateTimeFormat.forPattern("HH:mm");
System.out.println(airTime1);
System.out.println(startTime1);
Minutes difference = ((Minutes.minutesBetween(startTime1,airTime1)));
String differenceS = String.valueOf(difference);
System.out.println(differenceS);
LocalTime remaining1 = formatter.parseLocalTime(differenceS);
System.out.println(remaining1);
airTime1 & startTime1 are both localTime variables. difference should contain the duration between the two times. differenceS is a String representation of difference, as minutes cannot be converted to String.
When I enter times into the variables such as 12:00 & 13:00, the variables are recorded as: 12:00:00.000 & 13:00:00.000, but differenceS received a value of PT-60M, which obviously throws an error. Does anyone know why the minutes difference line could be calculating this value?
Thanks in advance!
The Minutes class of jodatime overwrites the toString() method in a way that returns a String in ISO8601 duration format as mentioned in the JavaDoc. This is exactly what your PT-60M represents. A duration of -60 minutes.
If you just want the raw minutes printed your code could look like this:
DateTimeFormatter formatter = DateTimeFormat.forPattern("HH:mm");
System.out.println(airTime1);
System.out.println(startTime1);
Minutes difference = Minutes.minutesBetween(startTime1,airTime1);
System.out.println(Math.abs(difference.getMinutes()));
I faced with an interesting problem with mktime function. I use russian time zone (UTC+03:00) Волгоград, Москва, Санкт-Петербург (RTZ 2) / Volgograd, Moscow, Saint Petersburg/ and try to construct time_t for "7.01.2009 00:00:00"
tm localTM;
localTM.tm_sec = 0;
localTM.tm_min = 0;
localTM.tm_hour = 0;
localTM.tm_mday = 7;
localTM.tm_mon = 0;
localTM.tm_year = 109;
time_t t = mktime(&localTM);
After mktime execution date&time is changed to "6.01.2009 23:00:00".
I have no problems then I construct time for "06.01.2009 00:00:00" or "08.01.2009 00:00:00".
If I switch time zone to another one, I get no problems with "7.01.2009 00:00:00".
What can be a reason of this oddity, and how can I workaround the issue?
When performing conversion to time_t, mktime needs to guess if the input is DST (Daylight Saving Time) or not.
For that, tm.tm_isdst field is used. See from man mktime
tm_isdst A flag that indicates whether daylight saving time is in
effect at the time described. The value is positive if day-
light saving time is in effect, zero if it is not, and nega-
tive if the information is not available.
Since you do not initialize tm_isdst in your code, the default value (0) is used, making mktime think it's in NO-DST period.
To fix it in your code, simply add
localTM.tm_isdst = -1
Note - that logic is necessary as for some moments in time just the "wallclock" information stored in tm is not sufficient to determine the exact time.
And yes, the fact that the default behavior is like that is a bit messed up :)
Suppose I have an ISO 8601 duration, expressed as "P1M". Phrased colloquially, this means "one month." Is there a standard rule for converting this into a number of seconds, assuming the start date is not known?
For 30-day months, it might be 2,592,000.
For 31-day months, it might be 2,678,400.
In February, it might be 2,419,200 or it might be 2,505,600.
My gut says there's no way to resolve "one month" to an exact number of seconds without knowing context, and where those seconds are laid out on the calendar. But are there standard rules/conventions to calculate these durations in an abstract way?
From ISO 8601 documentation that I found (page 6 - http://xml.coverpages.org/ISO-FDIS-8601.pdf), it seems you are correct in that the number of seconds in a month cannot definitively be determined. However it does note that "In certain applications a month is regarded as a unit of time of 30 days", so depending on your application this may be a valid approach.
The distinction between "Calendar Time" (Years, Months, etc) and "Absolute Time" (Hours, Minutes, Seconds, etc) is sometimes an important one. As an example, some people might complain about having 13 mortgage payments some years if they paid every 30 days as opposed to every month.
You are right, an ISO 8601 duration is dependent of the context.
A duration is a period/an interval of time between two dates.
Example :
2020-01-01/2020-02-01 = P1M = P31D
2020-02-01/2020-03-01 = P1M = P29D
2019-02-01/2019-03-01 = P1M = P28D
If you want a fixed duration indepedent of the context, use the day notation P30D, P60D, P90D... instead.
The same applies for years :
2019-01-01/2020-01-01 = P1Y = P12M = P365D
2020-01-01/2021-01-01 = P1Y = P12M = P366D
If you can't have context information about a duration, for example P1M retrieved from database or given by user input, use by default today's context.
//What is a duration of one month in seconds ?
P1M = ? (no context)
//Use default context
Today = 2020-03-31
2020-03-31/P1M = 2020-03-31/2020-04-30
=> P1M = P30D
//A month contains 2 592 000 seconds
What is the purpose of having Date and Time classes when there is a DateTime class that can handle both?
To summarize what the common ruby time classes are:
Time
This is the basic workhorse core ruby time class.
Has date and time attributes (year, month, day, hour, min, sec, subsec)
Based on floating-point second intervals from unix epoch (1970-01-01)
Can handle negative times before unix epoch
Can handle time arithmetic in units of seconds
Natively works in either UTC or "local" (system time zone)
There are really 3 kinds of Time object when it comes to dealing with time zones, let's look at a summer time to show DST:
utc = Time.utc(2012,6,1) # => 2012-12-21 00:00:00 UTC
utc.zone # => "UTC"
utc.dst? # => false
utc.utc? # => true
utc.utc_offset # => 0
local = Time.local(2012,6,1) # => 2012-06-01 00:00:00 -0700
local.zone # => "PDT"
local.dst? # => true
local.utc? # => false
local.utc_offset # => -25200
nonlocal = Time.new(2012,6,1,0,0,0, "-07:00") # => 2012-06-01 00:00:00 -0700
nonlocal.zone # => nil
nonlocal.dst? # => false
nonlocal.utc? # => false
nonlocal.utc_offset # => -25200
The last 2 look similar, but beware: you should not do arithmetic with a non-local Time. This is simply a time with a UTC offset and no zone, so it doesn't know the rules of DST. Adding time over the DST boundary will not change the offset and the resulting time-of-day will be wrong.
ActiveSupport::TimeWithZone
This one is worth mentioning here since it's what you use in Rails. Same as Time, plus:
Can handle any time zone
Respects DST
Can convert times between zones
I generally always reach for this when ActiveSupport is available as it takes care of all the time zone pitfalls.
Date
Has date attributes only (year, month, day)
Based on integer whole-day intervals from an arbitrary "day zero" (-4712-01-01)
Can handle date arithmetic in units of whole days
Can convert between dates in the ancient Julian calendar to modern Gregorian
Date is more useful than Time whenever you deal in whole days: no time zones to worry about! (I'm surprised this doesn't deal with the modern Persian calendar since it knows about the obsolete Julian calendar from centuries ago.)
DateTime
Has date and time attributes (year, month, day, hour, min, sec)
Based on fractions of whole-day intervals from an arbitrary "day zero" (-4712-01-01)
Can handle date arithmetic in units of whole days or fractions
Personally, I never have reason to use this: it's slow, it handles time without considering time zones, and it has an inconsistent interface. I find it leads to confusion whenever you assume you have a Time-like object, but it actually behaves like a Date instead:
Time.new(2012, 12, 31, 0, 0, 0) + 1 == Time.new(2012, 12, 31, 0, 0, 1)
DateTime.new(2012, 12, 31, 0, 0, 0) + 1 == DateTime.new(2013, 1, 1, 0, 0, 0)
Further, it has a meaningless "zone" attribute (note how non-local Time objects warn you that zone == nil), and you can't know anything else about it before turning it into a Time first:
dt = DateTime.new(2012,12,6, 1, 0, 0, "-07:00")
dt.zone # => "-07:00"
dt.utc? # => NoMethodError: undefined method `utc?'
dt.dst? # => NoMethodError: undefined method `dst?'
dt.utc_offset # => NoMethodError: undefined method `utc_offset'
Dealing with microseconds to check for rounding is also a little strange. You would think that because it doesn't have a usec attribute that it only deals in whole numbers, but you'd be wrong:
DateTime.now.usec # => NoMethodError: undefined method `usec'
DateTime.now.to_time.usec => 629399
In short, unless you're dealing with astronomical events in the ancient past and need to convert the Julian date (with time of day) to a modern calendar, please don't use DateTime. If anyone has an actual use case for this class, I'd love to read your comments.
I know there is an accepted answer but I have something to add. The Date class is a heavyweight, academic strength class. It can handle all sorts of RFC's, parse the strangest things and converts julian dates from thousand years ago to gregorian with the reform date of choice. The Time class is lightweight and it does not know of any of this stuff. It's cheaper and that shows up in a benchmark:
require 'benchmark'
require 'date'
Benchmark.bm(10) do |x|
x.report('date'){100000.times{Date.today} }
x.report('datetime'){100000.times{DateTime.now} }
x.report('time'){100000.times{Time.now} }
end
Result:
user system total real
date 1.250000 0.270000 1.520000 ( 1.799531)
datetime 6.660000 0.360000 7.020000 ( 7.690016)
time 0.140000 0.030000 0.170000 ( 0.200738)
(Ruby 1.9.2)
DateTime is a subclass of Date, so whatever you can do with Date can be done with DateTime. But as tadman and steenslag point out, DateTime is slower. See steenslag's answer for how much slower it is.
With respect to DateTime vs, Time, I found something here:
Time is a wrapper around Unix-Epoch.
Date (and DateTime) use rational and a "day zero" for storage. So Time is faster but the upper and lower bounds are tied to epoch time (which for 32bit epoch times is something around 1970-2040...while Date (and DateTime) have an almost infinite range but are terribly slow.
In short, DateTime is an all around superstar, and should be preferred in general, but if you want to optimize to the last bit, using Time can improve performance.
Another way of thinking of this is that Date and DateTime model time in terms of clocks and calendars, which is useful for describing times to users, and scheduling events. Having a Date without a time is nice for when you don't care about the time, and you don't want to think about time zones.
Time models time as a continuum, and is a wrapper around the Unix timestamp, which is just an integer. This is useful for all manner of internal applications where the computer doesn't care much whether a calendar boundary has been crossed, but just how many seconds (or milliseconds) have elapsed.
Yes. Date handles only the date for something, I.E., March 31, 1989. But it does not handle Time, for example, 12:30 PM.
DateTime, can handle both, March 31, 1989 12:30 PM EST.
Sometimes you don't need all parts of the DateTime. For example, you wanted to know when the use signed up for you website, Date would be useful here, because the time is eventually irrelevant.
In some cases you might want just the time. For example, if it's lunch time, you may want to tell the user your office is closed. At this point, the Data is irrelevant.
However, in most cases DateTime is used, because it can be used as either date, time, or both.
I have 2 independent but contiguous date ranges. The first range is the start and end date for a project. Lets say start = 3/21/10 and end = 5/16/10. The second range is a month boundary (say 3/1/10 to 3/31/10, 4/1/10 to 4/30/10, etc.) I need to figure out how many days in each month fall into the first range.
The answer to my example above is March = 10, April = 30, May = 16.
I am trying to figure out an excel formula or VBA function that will give me this value.
Any thoughts on an algorithm for this? I feel it should be rather easy but I can't seem to figure it out.
I have a formula which will return TRUE/FALSE if ANY part of the month range is within the project start/end but not the number of days. That function is below.
return month_start <= project_end And month_end >= project_start
Think it figured it out.
=MAX( MIN(project_end, month_end) - MAX(project_start,month_start) + 1 , 0 )