strptime: Parse and Format Date-time Objects

Description

Note that the date-time processing functions in stringx are a work in progress. Feature requests/comments/remarks are welcome.

strptime parses strings representing date-time data and converts it to a date-time object.

strftime formats a date-time object and outputs it as a character vector.

The functions are meant to be compatible with each other, especially with regards to formatting/printing. This is why they return/deal with objects of a new class, POSIXxt, which expends upon the built-in POSIXct.

Usage

strptime(x, format, tz = "", lenient = FALSE, locale = NULL)
strftime(
  x,
  format = "%Y-%m-%dT%H:%M:%S%z",
  tz = attr(x, "tzone")[1L],
  usetz = FALSE,
  ...,
  locale = NULL
)
# S3 method for POSIXxt
format(
  x,
  format = "%Y-%m-%dT%H:%M:%S%z",
  tz = attr(x, "tzone")[1L],
  usetz = FALSE,
  ...,
  locale = NULL
)
is.POSIXxt(x)
as.POSIXxt(x, tz = "", ...)
# S3 method for POSIXt
as.POSIXxt(x, tz = attr(x, "tzone")[1L], ...)
# S3 method for POSIXxt
as.POSIXlt(x, tz = attr(x, "tzone")[1L], ..., locale = NULL)
# S3 method for default
as.POSIXxt(x, tz = "", ...)
# S3 method for POSIXxt
as.Date(x, ...)
# S3 method for Date
as.POSIXxt(x, ...)
# S3 method for character
as.POSIXxt(x, tz = "", format = NULL, ..., lenient = FALSE, locale = NULL)
# S3 method for POSIXxt
Ops(e1, e2)
# S3 method for POSIXxt
seq(from, to, by, length.out = NULL, along.with = NULL, ...)
# S3 method for POSIXxt
c(..., recursive = FALSE)
# S3 method for POSIXxt
rep(..., recursive = FALSE)

Value

strftime and format return a character vector (in UTF-8).

strptime, as.POSIXxt.Date, and asPOSIXxt.character return an object of class POSIXxt, which extends upon POSIXct, see also DateTimeClasses.

Subtraction returns an object of the class difftime, see difftime.

If a string cannot be recognised as valid date/time specifier (as per the given format string), the corresponding output will be NA.

Arguments

x: object to be converted: a character vector for strptime and as.POSIXxt.character, an object of class POSIXxt for strftime an object of class Date for as.POSIXxt.Date, or objects coercible to
format: character vector of date-time format specifiers, see stri_datetime_fstr; e.g., "%Y-%m-%d" or "datetime_full"; the default conforms to the ISO 8601 guideline
tz: NULL or '' for the default time zone (see stri_timezone_get) or a single string with a timezone identifier, see stri_timezone_list; note that when x is equipped with tzone attribute, this datum is used; as.POSIXxt.character treats dates as being at midnight local time
lenient: single logical value; should date/time parsing be lenient?
locale: NULL or '' for the default locale (see stri_locale_get) or a single string with a locale identifier, see stri_locale_list
usetz: not used (with a warning if attempting to do so) [DEPRECATED]
...: not used
e1, e2, from, to, by, length.out, along.with, recursive: arguments to c, rep, seq, etc.

Differences from Base R

Replacements for base strptime and strftime implemented with stri_datetime_parse and stri_datetime_format.

format.POSIXxt is a thin wrapper around strftime.

formatting/parsing date-time in different locales and calendars is difficult and non-portable across platforms [fixed here -- using services provided by ICU]
default format not conforming to ISO 8601, in particular not displaying the current time zone [fixed here]
only the names attribute in x is propagated [fixed here]
partial recycling with no warning [fixed here]
strptime returns an object of class POSIXlt, which is not the most convenient to work with, e.g., when including in data frames [fixed here]
Ideally, there should be only one class to represent dates and one to represent date/time; POSIXlt is no longer needed as we have stri_datetime_fields; our new POSIXxt class aims to solve the underlying problems with POSIXct's not being consistent with regards to working in different time zones and dates (see, e.g., as.Date(as.POSIXct(strftime(Sys.Date())))) [addressed here]
dates without times are not always treated as being at midnight (despite that being stated in the help page for as.POSIXct) [fixed here]
strftime does not honour the tzone attribute, which is used whilst displaying time (via format) [fixed here]

Author

Marek Gagolewski

Details

Note that the ISO 8601 guideline suggests a year-month-day date format and a 24-hour time format always indicating the effective time zone, e.g., 2015-12-31T23:59:59+0100. This is so as to avoid ambiguity.

When parsing strings, missing fields are filled based on today's midnight data.

Examples

Run this code

strftime(Sys.time())  # default format - ISO 8601
f <- c("date_full", "%Y-%m-%d", "date_relative_short", "datetime_full")
strftime(Sys.time(), f)  # current default locale
strftime(Sys.time(), f, locale="de_DE")
strftime(Sys.time(), "date_short", locale="en_IL@calendar=hebrew")
strptime("1970-01-01 00:00:00", "%Y-%m-%d %H:%M:%S", tz="GMT")
strptime("14 Nisan 5703", "date_short", locale="en_IL@calendar=hebrew")
as.POSIXxt("1970-01-01")
as.POSIXxt("1970/01/01 12:00")

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