This R package has three functions for dealing with dates.
parse_iso_8601
recognizes and parses all valid ISO 8601
date and time formats. It can also be used as an ISO 8601
validator.parse_date
can parse a date when you don’t know which
format it is in. First it tries all ISO 8601 formats. Then it tries
git’s versatile date parser. Lastly, it tries
as.POSIXct
.format_iso_8601
formats a date (and time) in specific
ISO 8601 format.The git parser does not work for dates before 1970 and after 2100. For these dates the current year is used instead:
library(parsedate)
parse_date("april 15 1971")
## [1] "1971-04-15 UTC"
parse_date("april 15 1969")
## [1] "2022-04-15 UTC"
parse_date("april 15 2110")
## [1] "2022-04-15 UTC"
parse_iso_8601
recognizes all valid ISO 8601 formats,
and gives an NA
for invalid dates. Here are some
examples
library(parsedate)
parse_iso_8601("2013-02-08 09")
## [1] "2013-02-08 09:00:00 UTC"
parse_iso_8601("2013-02-08 09:30")
## [1] "2013-02-08 09:30:00 UTC"
parse_iso_8601("2013-02-08T09")
## [1] "2013-02-08 09:00:00 UTC"
parse_iso_8601("2013-02-08T09:30")
## [1] "2013-02-08 09:30:00 UTC"
parse_iso_8601("2013-02-08T09:30:26")
## [1] "2013-02-08 09:30:26 UTC"
parse_iso_8601("2013-02-08T09:30:26.123")
## [1] "2013-02-08 09:30:26 UTC"
parse_iso_8601("2013-02-08T09:30.5")
## [1] "2013-02-08 09:30:30 UTC"
parse_iso_8601("2013-02-08T09,25")
## [1] "2013-02-08 09:15:00 UTC"
parse_iso_8601("2013-02-08T09:30:26Z")
## [1] "2013-02-08 09:30:26 UTC"
parse_iso_8601("2013-W06-5")
## [1] "2013-02-08 UTC"
parse_iso_8601("2013-W01-1")
## [1] "2012-12-31 UTC"
parse_iso_8601("2009-W01-1")
## [1] "2008-12-29 UTC"
parse_iso_8601("2009-W53-7")
## [1] "2010-01-03 UTC"
parse_iso_8601("2013-039")
## [1] "2013-02-08 UTC"
parse_iso_8601("2013-039 09:30:26Z")
## [1] "2013-02-08 09:30:26 UTC"
Sometimes one has to work with a large number of dates, in arbitrary
formats. It is of impossible to reliably guess the format of some dates,
because of ambiguity. But it is often not critical to get the date
exactly right in the ambiguous cases, and this is when the
parse_date
function is useful. It tries a large number of
formats, here is the algorithm is uses:
parse_iso_8601
.as.POSIXct
.
(It is unlikely that this step will parse any dates that the first two
steps couldn’t, but it is still a logical fallback, to make sure that we
can parse at least as many dates as as.POSIXct
.Here are some examples. The first ones are easy.
parse_date("2014-12-12")
## [1] "2014-12-12 UTC"
parse_date("04/15/99")
## [1] "1999-04-15 UTC"
parse_date("15/04/99")
## [1] "1999-04-15 UTC"
The following formats are ambiguous and are parsed as month/day/year.
parse_date("12/11/99")
## [1] "1999-12-11 UTC"
parse_date("11/12/99")
## [1] "1999-11-12 UTC"
parse_date("03/20")
## [1] "2022-03-20 UTC"
parse_date("12")
## [1] "2022-01-12 UTC"
But not for this, because this is ISO 8601.
parse_date("2014")
## [1] "2014-01-01 UTC"
The format_iso_8601
function formats a date (and time)
in a fixed format that is ISO 8601 valid, and can be used to compare
dates as character strings. It converts the date(s) to UTC.
format_iso_8601(parse_iso_8601("2013-02-08"))
## [1] "2013-02-08T00:00:00+00:00"
format_iso_8601(parse_iso_8601("2013-02-08 09:34:00"))
## [1] "2013-02-08T09:34:00+00:00"
format_iso_8601(parse_iso_8601("2013-02-08 09:34:00+01:00"))
## [1] "2013-02-08T08:34:00+00:00"
format_iso_8601(parse_iso_8601("2013-W06-5"))
## [1] "2013-02-08T00:00:00+00:00"
format_iso_8601(parse_iso_8601("2013-039"))
## [1] "2013-02-08T00:00:00+00:00"