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.

### 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")

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