These 53 week years occur on all years that have Thursday as the 1st of January and on leap years that start on Wednesday the 1st. That is 364 or 371 days instead of the usual 365 or 366 days.
Iso 8601 full#
An average year is exactly 52.1775 weeks long months ( 1⁄ 12 year) average at exactly 4.348 125 weeks.Īn ISO week-numbering year (also called ISO year informally) has 52 or 53 full weeks. In every cycle there are 71 years with an additional 53rd week (corresponding to the Gregorian years that contain 53 Thursdays). The Gregorian leap cycle, which has 97 leap days spread across 400 years, contains a whole number of weeks ( 20 871). The system specifies a week year atop the Gregorian calendar by defining a notation for ordinal weeks of the year. This was previously known as "Industrial date coding". It is used (mainly) in government and business for fiscal years, as well as in timekeeping. The ISO week date system is effectively a leap week calendar system that is part of the ISO 8601 date and time standard issued by the International Organization for Standardization (ISO) since 1988 (last revised in 2019) and, before that, it was defined in ISO (R) 2015 since 1971.
Iso 8601 code#
It should be clear from the all the code examples that even though ISO 8601 supports arbitrary precision dates, the libraries around it don’t, partially because a 1GHz processor has a clock rate of 1ns, so recording a higher precision is rare and unlikely. Nanosecond precision is as granular as one should go. Recommendationīefore committing to a custom date format, check if ISO 8601 doesn’t already cover it. This may be the strongest argument to write a custom parser, though it is certainly possible to determine precision with custom Java 8 (and by extension Threeten) datetime formatters. If someone sends in a “2016-06” for a birthdate the client should have the opportunity to reject it because the date is not precise enough. Notice that none of the date parsing libraries showcased, outside of date4j (and arguably Numpy) kept track of precision.īut I can understand some situations where precision is wanted. DAYS )) īy eschewing retention of the parsed precision, it’s easier to support standard parsing mechanisms. parse ( "T10:30", formatter ) ĪssertThat (hour. parse ( "T10:00", formatter ) final LocalDateTime minute = LocalDateTime. ISO_LOCAL_DATE_TIME final LocalDateTime hour = LocalDateTime. Here’s are a couple of ways to represent this model (I’m using F# because the implementation is the shortest!)įinal DateTimeFormatter formatter = DateTimeFormatter. For instance, 2016 would be tagged with a precision of Year and 2016-01 would be tagged with Month. Sometimes one wants to keep track the precision of the data. If the only reason for not using the Java8 time classes is that it requires Java8 then Threeten seems an appropriate fit. ?Īnyone familiar with Java8 time module will be familiar with Threeten. JSON does not specify how dates should be formatted, so fhir defines it for us as a regular expression ( visualized): One of the jobs that fhir has is to define models described in JSON to improve interoperability and part of these models include dates. As an example I will use ISO 8601, which is a standard way to represent a datetime with arbitrary precision (obligatory xkcd).īefore we get to the examples, the impetus for this post comes from an emerging healthcare standard called fhir (it’s pronounced “fire” and is an acronym but I prefer writing in lowercase). In situations like these, I like to look at current standards and see how implementations work. Given a date format that supports arbitrary precision, the question of how best to represent the date in a language of choice is generally tough to answer. ISO 8601 and Nanosecond Precision Across Languages Published on: JIntroduction