as.Date
Date-Time Parsing

### Description

Functions for converting S objects (for example, character strings) to date-time objects.

### Usage

    as.Date(x, ...)
    ## Default S3 method:
    as.Date(x, ...)
    ## S3 method for class 'numeric':
    as.Date(x, origin, ...)
    ## S3 method for class 'character':
    as.Date(x, format = "", ...)
    ## S3 method for class 'factor':
    as.Date(x, ...)
    ## S3 method for class 'POSIXct':
    as.Date(x, tz = "UTC", ...)
    ## S3 method for class 'POSIXlt':
    as.Date(x, ...)
    ## S3 method for class 'date':
    as.Date(x, ...)
    ## S3 method for class 'dates':
    as.Date(x, ...)
    as.POSIXct(x, tz = "", ...)
    ## Default S3 method:
    as.POSIXct(x, tz = "", ...)
    ## S3 method for class 'numeric':
    as.POSIXct(x, tz = "", origin, ...)
    ## S3 method for class 'Date':
    as.POSIXct(x, ...)
    ## S3 method for class 'factor':
    as.POSIXct(x, ...)
    ## S3 method for class 'POSIXlt':
    as.POSIXct(x, tz = "", ...)
    ## S3 method for class 'date':
    as.POSIXct(x, ...)
    ## S3 method for class 'dates':
    as.POSIXct(x, ...)
    as.POSIXlt(x, tz = "", ...)
    ## Default S3 method:
    as.POSIXlt(x, tz = "", ...)
    ## S3 method for class 'numeric':
    as.POSIXlt(x, tz = "", origin, ...)
    ## S3 method for class 'character':
    as.POSIXlt(x, tz = "", format, ...)
    ## S3 method for class 'factor':
    as.POSIXlt(x, ...)
    ## S3 method for class 'Date':
    as.POSIXlt(x, ...)
    ## S3 method for class 'POSIXct':
    as.POSIXlt(x, tz = "", ...)
    ## S3 method for class 'date':
    as.POSIXlt(x, ...)
    ## S3 method for class 'dates':
    as.POSIXlt(x, ...)
    strptime(x, format, tz = "")
    as.difftime(tim, format = "%X", units = "auto")

### Arguments

x | any object to be converted to date-time.
format | a character string specifying the date-time format; for example, "%Y-%m-%d" "%Y-%m-%d %H:%M" "%Y-%m-%d %H:%M:%S" "%Y-%m-%d %H:%M:%OS" "%Y-%m-%d %H:%M:%OS3"
tz | a character string specifying the time zone.
origin | a character string specifying the starting date-time. Must be provided for the numeric methods.
tim | any object to be converted to difftime. Usually character or numeric.
units | a character string specifying the time unit from "auto", "secs", "mins", "hours", "days", and "weeks".
... | additional arguments.

### Details

The Spotfire Enterprise Runtime for R parsing routines are significantly faster when parsing date and time strings if the format argument only contains the control sequences %Y, %y, %m, %d, %H, %M, %S, or %OS. If the format argument contains other control sequences, or the string cannot be parsed, parsing can be much slower.
Value

as.Date.* | return a Date object representing the date.
as.POSIXct.* | return a POSIXct object representing the date-time.
as.POSIXlt.* | return a POSIXlt object representing the date-time.
strptime | return a POSIXlt object representing the date-time.
as.difftime | returns a difftime object representing the time interval.

References
2004, 1988, 1997, ... ISO 8601. Data elements and interchange formats -- Information interchange -- Representation of dates and times. Geneva, Switzerland: International Organization for Standardization.
For links to versions available on-line see (at the time of writing) http://www.qsl.net/g1smd/isopdf.htm.
For information on the current official version, see (at the time of writing) http://www.iso.org/iso/en/prods-services/popstds/datesandtime.html.
http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/windows_tzid.html.
See Also
Date, POSIXt, format.Date, difftime
Examples

    ## convert to Date
    as.Date(c("1900.01.01", "1970-01-01 00:00:00", "2038/01/19 03:14:08"))
    as.Date("01/19/2038 03:14:08", format = "%m/%d/%Y %H:%M:%S")
    as.Date(-1:1, origin = "1970-01-01")
    as.Date(-1:1, origin = "1970-01-01 00:00:00")
    as.Date(Sys.time())
    as.Date(Sys.time(), tz = "Asia/Shanghai")
    ## convert to POSIXct
    as.POSIXct(c("1900.01.01", "1970-01-01 00:00:00",
       "2038/01/19 03:14:08"))
    as.POSIXct("01/19/2038 03:14:08", format = "%m/%d/%Y %H:%M:%S",
       tz = "Asia/Shanghai")
    as.POSIXct(-1:1, origin = "1970-01-01")
    as.POSIXct(-1:1, origin = "1970-01-01 00:00:00", tz = "Asia/Shanghai")
    as.POSIXct(Sys.Date())
    ## convert to POSIXlt
    as.POSIXlt(c("1900.01.01", "1970-01-01 00:00:00",
       "2038/01/19 03:14:08"))
    as.POSIXlt("01/19/2038 03:14:08", format = "%m/%d/%Y %H:%M:%S",
       tz = "Asia/Shanghai")
    as.POSIXlt(-1:1, origin = "1970-01-01")
    as.POSIXlt(-1:1, origin = "1970-01-01 00:00:00", tz = "Asia/Shanghai")
    as.POSIXlt(-1:1, origin = "1970-01-01 00:00:00", tz = "GMT")
    as.POSIXlt(Sys.time())
    as.POSIXlt(Sys.time(), tz = "Asia/Shanghai")
    as.POSIXlt(Sys.time(), tz = "GMT")
    as.POSIXlt(Sys.Date())
    ## convert to POSIXlt with strptime
    strptime(c("1900.01.01", "1970-01-01 00:00:00", "2038/01/19 03:14:08"),
       format = "")
    strptime("01/19/2038 03:14:08", format = "%m/%d/%Y %H:%M:%S",
       tz = "Asia/Shanghai")
    strptime(Sys.time(), format = "")
    strptime(Sys.time(), format = "%Y-%m-%d %H:%M:%S")
    strptime(Sys.Date(), format = "")
    ## parse strings and numerics into difftime objects
    as.difftime("0:1:0", format = "%H:%M:%S", units = "secs")
    as.difftime("1", format = "%M", units = "secs")
    as.difftime(1, units = "secs")

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