format.Date {base}R Documentation

Date Conversion Functions to and from Character

Description

Functions to convert between character representations and objects of class "Date" representing calendar dates.

Usage

as.Date(x, ...)
## S3 method for class 'character':
as.Date(x, format = "", ...)

## S3 method for class 'Date':
format(x, ...)

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

Arguments

x An object to be converted.
format A character string. The default is "%Y-%m-%d". For details see strftime.
... Further arguments to be passed from or to other methods, including format for as.character and as.Date methods.

Details

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 as.Date methods accept character strings, factors, logical NA and objects of classes "POSIXlt" and "POSIXct". (The last are converted to days by ignoring the time after midnight in the representation of the time in UTC.) Also objects of class "date" (from package date or survival) and "dates" (from package chron).

The format and as.character methods ignore any fractional part of the date.

Value

The format and as.character methods return a character vector representing the date.
The as.Date methods return an object of class "Date".

Note

The default formats follow the rules of the ISO 8601 international standard which expresses a day as "2001-02-03".

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 a missing year, month or day is the current one. If it specifies a date incorrectly, reliable implementations will give an error and the date is reported as NA. Unfortunately some common implementations (such as glibc) are unreliable and guess at the intended meaning.

Years before 1CE (aka 1AD) will probably not be handled 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

Date for details of the date class; locales to query or set a locale.

Your system's help pages on strftime and strptime to see how to specify their formats. Windows users will find no help page for strptime: code based on glibc is used (with corrections), so all the format specifiers described here are supported, but with no alternative number representation nor era available in any locale.

Examples

## locale-specific version of the date
format(Sys.Date(), "%a %b %d")

## 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 <- as.Date(x, "%d%b%Y")
## Sys.setlocale("LC_TIME", lct)
z

## read in date/time info in format 'm/d/y'
dates <- c("02/27/92", "02/27/92", "01/14/92", "02/28/92", "02/01/92")
as.Date(dates, "%m/%d/%y")

[Package base version 2.1.0 Index]