Functions to convert between character representations and objects of
"POSIXct" representing calendar
dates and times.
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An object to be converted: a character vector for
A character string specifying the time zone to be used for
the conversion. System-specific (see
A character string. The default for the
Further arguments to be passed from or to other methods.
logical. Should the time zone abbreviation be appended
to the output? This is used in printing times, and more reliable
as.character methods and
convert objects from the classes
"POSIXct" to character vectors.
strptime converts character vectors to class
x is first converted by
Each input string is processed as far as necessary for the format
specified: any trailing characters are ignored.
strftime is a wrapper for
format.POSIXlt, and it and
format.POSIXct first convert to class
as.POSIXlt (so they also work for class
"Date"). Note that only that conversion depends on the
The usual vector re-cycling rules are applied to
format so the answer will be of length of the longer of these
Locale-specific conversions to and from character strings are used
where appropriate and available. This affects the names of the days
and months, the AM/PM indicator (if used) and the separators in
formats such as
%X, via the setting of the
LC_TIME locale category. The ‘current locale’ of
the descriptions might mean the locale in use at the start of the R
session or when these functions are first used.
The details of the formats are platform-specific, but the following are
likely to be widely available: most are defined by the POSIX standard.
A conversion specification is introduced by
followed by a single letter or
E and then a single
letter. Any character in the format string not part of a conversion
specification is interpreted literally (and
%). Widely implemented conversion specifications include
Abbreviated weekday name in the current locale on this platform. (Also matches full name on input: in some locales there are no abbreviations of names.)
Full weekday name in the current locale. (Also matches abbreviated name on input.)
Abbreviated month name in the current locale on this platform. (Also matches full name on input: in some locales there are no abbreviations of names.)
Full month name in the current locale. (Also matches abbreviated name on input.)
Date and time. Locale-specific on output,
"%a %b %e %H:%M:%S %Y" on input.
Century (00–99): the integer part of the year divided by 100.
Day of the month as decimal number (01–31).
Date format such as
%m/%d/%y: the C99
standard says it should be that exact format (but not all OSes
Day of the month as decimal number (1–31), with a leading space for a single-digit number.
Equivalent to %Y-%m-%d (the ISO 8601 date format).
The last two digits of the week-based year
%V). (Accepted but ignored on input.)
The week-based year (see
%V) as a decimal
number. (Accepted but ignored on input.)
Hours as decimal number (00–23). As a special exception strings such as 24:00:00 are accepted for input, since ISO 8601 allows these.
Hours as decimal number (01–12).
Day of year as decimal number (001–366).
Month as decimal number (01–12).
Minute as decimal number (00–59).
Newline on output, arbitrary whitespace on input.
AM/PM indicator in the locale. Used in
%I and not with
empty string in some locales (and the behaviour is undefined if
used for input in such a locale).
Some platforms accept
%P for output, which uses a lower-case
version: others will output
The 12-hour clock time (using the locale's AM or PM). Only defined in some locales.
Second as integer (00–61), allowing for up to two leap-seconds (but POSIX-compliant implementations will ignore leap seconds).
Tab on output, arbitrary whitespace on input.
Weekday as a decimal number (1–7, Monday is 1).
Week of the year as decimal number (00–53) using Sunday as the first day 1 of the week (and typically with the first Sunday of the year as day 1 of week 1). The US convention.
Week of the year as decimal number (01–53) as defined in ISO 8601. If the week (starting on Monday) containing 1 January has four or more days in the new year, then it is considered week 1. Otherwise, it is the last week of the previous year, and the next week is week 1. (Accepted but ignored on input.)
Weekday as decimal number (0–6, Sunday is 0).
Week of the year as decimal number (00–53) using Monday as the first day of week (and typically with the first Monday of the year as day 1 of week 1). The UK convention.
Date. Locale-specific on output,
"%y/%m/%d" on input.
Time. Locale-specific on output,
"%H:%M:%S" on input.
Year without century (00–99). On input, values 00 to 68 are prefixed by 20 and 69 to 99 by 19 – that is the behaviour specified by the 2004 and 2008 POSIX standards, but they do also say ‘it is expected that in a future version the default century inferred from a 2-digit year will change’.
Year with century. Note that whereas there was no zero in the original Gregorian calendar, ISO 8601:2004 defines it to be valid (interpreted as 1BC): see https://en.wikipedia.org/wiki/0_(year). Note that the standards also say that years before 1582 in its calendar should only be used with agreement of the parties involved.
For input, only years
0:9999 are accepted.
Signed offset in hours and minutes
from UTC, so
-0800 is 8 hours behind UTC. Values up to
+1400 are accepted. (Standard only for output.)
(Output only.) Time zone abbreviation as a character string (empty if not available). This may not be reliable when a time zone has changed abbreviations over the years.
Where leading zeros are shown they will be used on output but are
optional on input. Names are matched case-insensitively on input:
whether they are capitalized on output depends on the platform and the
locale. Note that abbreviated names are platform-specific (although
the standards specify that in the C locale they must be the
first three letters of the capitalized English name: this convention
is widely used in English-language locales but for example the French
month abbreviations are not the same on any two of Linux, macOS, Solaris
and Windows). Knowing what the abbreviations are is essential
if you wish to use
%h as part of an
input format: see the examples for how to check.
%Z is used for output with an
object with an assigned time zone an attempt is made to use the values
for that time zone — but it is not guaranteed to succeed.
Not in the standards and less widely implemented are
The 24-hour clock time with single digits preceded by a blank.
The 12-hour clock time with single digits preceded by a blank.
(Output only.) The number of seconds since the epoch.
(Output only.) Similar to
"%a %b %e %H:%M:%S %Z %Y". May depend on the locale.
For output there are also
%O[dHImMUVwWy] which may emit
numbers in an alternative locale-dependent format (e.g., roman
%E[cCyYxX] which can use an alternative
‘era’ (e.g., a different religious calendar). Which of these
are supported is OS-dependent. These are accepted for input, but with
the standard interpretation.
Specific to R is
%OSn, which for output gives the seconds
0 <= n <= 6 decimal places (and if
not followed by a digit, it uses the setting of
getOption("digits.secs"), or if that is unset,
0). Further, for
%OS will input seconds
including fractional seconds. Note that
%S does not read
fractional parts on output.
The behaviour of other conversion specifications (and even if other
character sequences commencing with
% are conversion
specifications) is system-specific. Some systems document that the
use of multi-byte characters in
format is unsupported: UTF-8
locales are unlikely to cause a problem.
format methods and
strftime return character vectors
representing the time.
NA times are returned as
NA_character_. The elements are restricted to 256 bytes, plus
a time zone abbreviation if
usetz is true. (On known platforms
longer strings are truncated at 255 or 256 bytes, but this is not
guaranteed by the C99 standard.)
strptime turns character representations into an object of
"POSIXlt". The time zone is used to set the
isdst component and to set the
"tzone" attribute if
tz != "". If the specified time is invalid (for example
"2010-02-30 08:00") all the components of the result are
NA. (NB: this does means exactly what it says – if it is an
invalid time, not just a time that does not exist in some time zone.)
Everyone agrees that years from 1000 to 9999 should be printed with 4 digits, but the standards do not define what is to be done outside that range. For years 0 to 999 most OSes pad with zeros or spaces to 4 characters, and Linux outputs just the number.
OS facilities will probably not print years before 1 CE (aka 1 AD)
‘correctly’ (they tend to assume the existence of a year 0: see
https://en.wikipedia.org/wiki/0_(year), and some OSes get them
completely wrong). Common formats are
Years after 9999 and before -999 are normally printed with five or more characters.
Some platforms support modifiers from POSIX 2008 (and others). On
Linux the format
"%04Y" assures a minimum of four characters
and zero-padding. The internal code (as used on Windows and by
default on macOS) uses zero-padding by default, and formats
%_Y can be used for space padding and no
Offsets from GMT (also known as UTC) are part of the conversion
between timezones and to/from class
"POSIXct", but cause
difficulties as they often computed incorrectly.
They conventionally have the opposite sign from time-zone
Sys.timezone): positive values are
East of the meridian. Although there have been time zones with
offsets like 00:09:21 (Paris in 1900), and 00:44:30 (Liberia until
1972), offsets are usually treated as whole numbers of minutes, and
are most often seen in RFC 822 email headers in forms like
-0800 (e.g., used on the Pacific coast of the US in winter).
%z can be used for input or output: it is a character
string, conventionally plus or minus followed by two digits for
hours and two for minutes: the standards say that an empty string
should be output if the offset is unknown, but some systems use the
offsets for the time zone in use for the current year.
The default formats follow the rules of the ISO 8601 international
standard which expresses a day as
"2001-02-28" and a time as
"14:01:02" using leading zeroes as here. (The ISO form uses no
space to separate dates and times: R does by default.)
strptime the input string need not specify the date
completely: it is assumed that unspecified seconds, minutes or hours
are zero, and an unspecified year, month or day is the current one.
(However, if a month is specified, the day of that month has to be
%e since the current day of the
month need not be valid for the specified month.) Some components may
be returned as
NA (but an unknown
tzone component is
represented by an empty string).
If the time zone specified is invalid on your system, what happens is system-specific but it will probably be ignored.
Remember that in most time zones some times do not occur and some
occur twice because of transitions to/from ‘daylight saving’
(also known as ‘summer’) time.
strptime does not
validate such times (it does not assume a specific time zone), but
as.POSIXct will do so. Conversion by
strftime and formatting/printing uses OS facilities and may
return nonsensical results for non-existent times at DST transitions.
In a C locale
%c is required to be
"%a %b %e %H:%M:%S %Y". As Windows does not comply (and
uses a date format not understood outside N. America), that format is
used by R on Windows in all locales.
International Organization for Standardization (2004, 2000, ...) ISO 8601. Data elements and interchange formats – Information interchange – Representation of dates and times. For links to versions available on-line see (at the time of writing) http://dotat.at/tmp/ISO_8601-2004_E.pdf and http://www.qsl.net/g1smd/isopdf.htm; for information on the current official version, see http://www.iso.org/iso/iso8601.
The POSIX 1003.1 standard, which is in some respects stricter than ISO 8601.
DateTimeClasses for details of the date-time classes; locales to query or set a locale.
Your system's help page on
strftime to see how to specify their
formats. (On some systems, including Windows,
replaced by more comprehensive internal code.)
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## locale-specific version of date() format(Sys.time(), "%a %b %d %X %Y %Z") ## time to sub-second accuracy (if supported by the OS) format(Sys.time(), "%H:%M:%OS3") ## read in date info in format 'ddmmmyyyy' ## This will give NA(s) in some locales; setting the C locale ## as in the commented lines will overcome this on most systems. ## lct <- Sys.getlocale("LC_TIME"); Sys.setlocale("LC_TIME", "C") x <- c("1jan1960", "2jan1960", "31mar1960", "30jul1960") z <- strptime(x, "%d%b%Y") ## Sys.setlocale("LC_TIME", lct) z ## read in date/time info in format 'm/d/y h:m:s' dates <- c("02/27/92", "02/27/92", "01/14/92", "02/28/92", "02/01/92") times <- c("23:03:20", "22:29:56", "01:03:30", "18:21:03", "16:56:26") x <- paste(dates, times) strptime(x, "%m/%d/%y %H:%M:%S") ## time with fractional seconds z <- strptime("20/2/06 11:16:16.683", "%d/%m/%y %H:%M:%OS") z # prints without fractional seconds op <- options(digits.secs = 3) z options(op) ## time zones name are not portable, but 'EST5EDT' comes pretty close. (x <- strptime(c("2006-01-08 10:07:52", "2006-08-07 19:33:02"), "%Y-%m-%d %H:%M:%S", tz = "EST5EDT")) attr(x, "tzone") ## An RFC 822 header (Eastern Canada, during DST) strptime("Tue, 23 Mar 2010 14:36:38 -0400", "%a, %d %b %Y %H:%M:%S %z") ## Make sure you know what the abbreviated names are for you if you wish ## to use them for input (they are matched case-insensitively): format(seq.Date(as.Date('1978-01-01'), by = 'day', len = 7), "%a") format(seq.Date(as.Date('2000-01-01'), by = 'month', len = 12), "%b")
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