This help topic is for R version 2.9.0. For the current version of R, try https://stat.ethz.ch/R-manual/R-patched/library/base/html/as.POSIXlt.html
as.POSIX* {base}R Documentation

Date-time Conversion Functions

Description

Functions to manipulate objects of classes "POSIXlt" and "POSIXct" representing calendar dates and times.

Usage

as.POSIXct(x, tz = "", ...)
as.POSIXlt(x, tz = "", ...)

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

## S3 method for class 'numeric'
as.POSIXlt(x, tz = "", origin, ...)

## S3 method for class 'POSIXlt'
as.double(x, ...)

Arguments

x

An object to be converted.

tz

A timezone specification to be used for the conversion, if one is required. System-specific (see time zones), but "" is the current timezone, and "GMT" is UTC (Universal Time, Coordinated).

...

further arguments to be passed to or from other methods.

format

character string giving a date-time format as used by strptime.

origin

a date-time object, or something which can be coerced by as.POSIXct(tz="GMT") to such an object.

Details

The as.POSIX* functions convert an object to one of the two classes used to represent date/times (calendar dates plus time to the nearest second). They can convert a wide variety of objects, including objects of the other class and of classes "Date", "date" (from package date or survival), "chron" and "dates" (from package chron) to these classes. Dates without times are treated as being at midnight UTC.

They can also convert character strings of the formats "2001-02-03" and "2001/02/03" optionally followed by white space and a time in the format "14:52" or "14:52:03". (Formats such as "01/02/03" are ambiguous but can be converted via a format specification by strptime.) Fractional seconds are allowed. Alternatively, format can be specified for character vectors or factors: if it is not specified and no standard format works for the first non-NA input an error is thrown.

Logical NAs can be converted to either of the classes, but no other logical vectors can be.

The as.double method converts "POSIXlt" objects to "POSIXct".

If you are given a numeric time as the number of seconds since an epoch, see the examples.

Value

as.POSIXct and as.POSIXlt return an object of the appropriate class. If tz was specified, as.POSIXlt will give an appropriate "tzone" attribute.

Note

If you want to extract specific aspects of a time (such as the day of the week) just convert it to class "POSIXlt" and extract the relevant component(s) of the list, or if you want a character representation (such as a named day of the week) use format.POSIXlt or format.POSIXct.

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

See Also

DateTimeClasses for details of the classes; strptime for conversion to and from character representations. Sys.timezone for details of the (system-specific)naming of time zones.

Examples

(z <- Sys.time())             # the current datetime, as class "POSIXct"
unclass(z)                    # a large integer
floor(unclass(z)/86400)       # the number of days since 1970-01-01
(z <- as.POSIXlt(Sys.time())) # the current datetime, as class "POSIXlt"
unlist(unclass(z))            # a list shown as a named vector

## suppose we have a time in seconds since 1960-01-01 00:00:00 GMT
z <- 1472562988
# ways to convert this
as.POSIXct(z, origin="1960-01-01")                # local
as.POSIXct(z, origin="1960-01-01", tz="GMT")      # in UTC
as.POSIXct(z, origin=ISOdatetime(1960,1,1,0,0,0)) # local
ISOdatetime(1960,1,1,0,0,0) + z                   # local

## SPSS dates (R-help 2006-02-16)
z <- c(10485849600, 10477641600, 10561104000, 10562745600)
as.Date(as.POSIXct(z, origin="1582-10-14", tz="GMT"))

as.POSIXlt(Sys.time(), "GMT") # the current time in UTC
## Not run: ## These may not be correct names on your system
as.POSIXlt(Sys.time(), "America/New_York")  # in New York
as.POSIXlt(Sys.time(), "EST5EDT")           # alternative.
as.POSIXlt(Sys.time(), "EST" )   # somewhere in Eastern Canada
as.POSIXlt(Sys.time(), "HST")    # in Hawaii
as.POSIXlt(Sys.time(), "Australia/Darwin")

## End(Not run)

[Package base version 2.9.0 ]