| as.POSIX* {base} | R Documentation |
Functions to manipulate objects of classes "POSIXlt" and
"POSIXct" representing calendar dates and times.
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, ...)
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. |
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.
as.POSIXct and as.POSIXlt return an object of the
appropriate class. If tz was specified, as.POSIXlt
will give an appropriate "tzone" attribute.
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.
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.
(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)