strptime {base}

R Documentation

Date-time Conversion Functions to and from Character

Description

Functions to convert between character representations and objects of classes "POSIXlt" and "POSIXct" representing calendar dates and times.

Usage

format.POSIXct(x, format = "", tz = "", usetz = FALSE, ...)
format.POSIXlt(x, format = "", usetz = FALSE, ...)

## S3 method for class 'POSIXt'
as.character(x, ...)

strftime(x, format="%Y-%m-%d %X", usetz = FALSE, ...)
strptime(x, format)

ISOdatetime(year, month, day, hour, min, sec, tz = "")
ISOdate(year, month, day, hour = 12, min = 0, sec = 0, tz = "GMT")

Arguments

x	An object to be converted.
tz	A timezone specification to be used for the conversion. System-specific, but "" is the current time zone, and "GMT" is UTC.
format	A character vector. The default is "%Y-%m-%d %H:%M:%S" if any component has a time component which is not midnight, and "%Y-%m-%d" otherwise.
...	Further arguments to be passed from or to other methods.
usetz	logical. Should the timezone be appended to the output? This is used in printing time, and as a workaround for problems with using "%Z" on most Linux systems.
year, month, day	numerical values to specify a day.
hour, min, sec	numerical values for a time within a day.

Details

strftime is an alias for format.POSIXlt, and format.POSIXct first converts to class "POSIXct" by calling as.POSIXct. Note that only that conversion depends on the time zone.

The usual vector re-cycling rules are applied to x and format so the answer will be of length that of the longer of the vectors.

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 and %X.

The details of the formats are system-specific, but the following are defined by the POSIX standard for strftime and are likely to be widely available. Any character in the format string other than the % escapes is interpreted literally (and %% gives %).

%a

Abbreviated weekday name.

%A

Full weekday name.

%b

Abbreviated month name.

%B

Full month name.

%c

Date and time, locale-specific.

%d

Day of the month as decimal number (01–31).

%H

Hours as decimal number (00–23).

%I

Hours as decimal number (01–12).

%j

Day of year as decimal number (001–366).

%m

Month as decimal number (01–12).

%M

Minute as decimal number (00–59).

%p

AM/PM indicator in the locale. Used in conjuction with %I and not with %H.

%S

Second as decimal number (00–61), allowing for up to two leap-seconds.

%U

Week of the year as decimal number (00–53) using the first Sunday as day 1 of week 1.

%w

Weekday as decimal number (0–6, Sunday is 0).

%W

Week of the year as decimal number (00–53) using the first Monday as day 1 of week 1.

%x

Date, locale-specific.

%X

Time, locale-specific.

%y

Year without century (00–99). If you use this on input, which century you get is system-specific. So don't! Often values up to 69 are prefixed by 20 and 70–99 by 19.

%Y

Year with century.

%Z

(output only.) Time zone as a character string (empty if not available). Note: do not use this on Linux unless the TZ environment variable is set.

Where leading zeros are shown they will be used on output but are optional on input.

ISOdatetime and ISOdate are convenience wrappers for strptime, that differ only in their defaults.

Value

The format methods and strftime return character vectors representing the time.

strptime turns character representations into an object of class "POSIXlt".

ISOdatetime and ISOdate return an object of class "POSIXct".

Note

The default formats follow the rules of the ISO 8601 international standard which expresses a day as "2001-02-03" and a time as "14:01:02" using leading zeroes as here. The ISO form uses no space to separate dates and times.

If the date string does not specify the date completely, the returned answer may be system-specific. The most common behaviour is to assume that unspecified seconds, minutes or hours are zero, and a missing year, month or day is the current one.

If the timezone specified is invalid on your system, what happens is system-specific but it will probably be ignored.

OS facilities will probably not print years before 1CE (aka 1AD) correctly.

References

International Organization for Standardization (1988, 1997, ...) ISO 8601. Data elements and interchange formats – Information interchange – Representation of dates and times. The 1997 version is available on-line at ftp://ftp.qsl.net/pub/g1smd/8601v03.pdf

See Also

DateTimeClasses for details of the date-time classes; locales to query or set a locale.

Your system's help pages on strftime and strptime to see how to specify their formats.

Examples

## locale-specific version of date()
format(Sys.time(), "%a %b %d %X %Y")
## we would include the timezone as in
## format(Sys.time(), "%a %b %d %X %Y %Z")
## but this crashes some Linux systems

## 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)
z <- strptime(x, "%m/%d/%y %H:%M:%S")
z

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