Parse POSIXct objects from input data
These function use the Boost Date_Time library to parse
datetimes (and dates) from strings, integers, factors or even numeric values
(which are cast to strings internally). They return a vector of
POSIXct objects (or
Date objects in the case of
POSIXct objects represent dates and time as (possibly
fractional) seconds since the ‘epoch’ of January 1, 1970.
A timezone can be set, if none is supplied ‘UTC’ is set.
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A vector of type character, integer or numeric with date(time) expressions to be parsed and converted.
A string with the timezone, defaults to the result of the (internal)
A logical value indicating if parsing should be to UTC; default is false implying localtime.
A number of fixed formats are tried in succession. These include
the standard ISO format ‘YYYY-MM-DD HH:MM:SS’ as well as
different local variants including several forms popular in the
United States. Two-digits years and clearly ambigous formats such
as ‘03/04/05’ are ignored. In the case of parsing failure
NA value is returned.
Fractional seconds are supported as well. As R itself only supports microseconds, the Boost compile-time option for nano-second resolution has not been enabled.
A vector of
POSIXct elements, or, in the case of
a vector of
By default, the (internal) conversion to (fractional) seconds since the epoch is relative to the locatime of this system, and therefore not completely independent of the settings of the local system. This is to strike a balance between ease of use and functionality. A more-full featured conversion could be possibly be added with support for arbitrary reference times, but this is (at least) currently outside the scope of this package. See the RcppCCTZ package which offers some timezone-shifting and differencing functionality. As of version 0.0.5 one can also parse relative to UTC avoiding the localtime issue,
Times and timezones can be tricky. This package offers a heuristic approach, it is likely that some input formats may not be parsed, or worse, be parsed incorrectly. This is not quite a Bobby Tables situation but care must always be taken with user-supplied input.
The Boost Date_Time library cannot parse single digit months or days. So while ‘2016/09/02’ works (as expected), ‘2016/9/2’ will not. Other non-standard formats may also fail.
The is a known issue (discussed at length in issue ticket 5) where Australian times are off by an hour. This seems to affect only Windows, not Linux.
When given a vector, R will coerce it to the type of the first
element. Should that be
NA, surprising things can
c(NA, Sys.Date()) forces both values to
numeric and the date will not be parsed correctly (as its
integer value becomes numeric before our code sees it). On the
c(Sys.Date(), NA) works as expected parsing as
type Date with one missing value. See
ticket 11) for more.
Operating System Impact
On Windows systems, accessing the
isdst flag on dates or times
before January 1, 1970, can lead to a crash. Therefore, the lookup of this
value has been disabled for those dates and times, which could therefore be
off by an hour (the common value that needs to be corrected).
It should not affect dates, but may affect datetime objects.
This StackOverflow answer provided the initial idea: http://stackoverflow.com/a/3787188/143305.
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## See the source code for a full list of formats, and the ## or the reference in help('anytime-package') for details times <- c("2004-03-21 12:45:33.123456", "2004/03/21 12:45:33.123456", "20040321 124533.123456", "03/21/2004 12:45:33.123456", "03-21-2004 12:45:33.123456", "2004-03-21", "20040321", "03/21/2004", "03-21-2004", "20010101") anytime(times) anydate(times) utctime(times) utcdate(times) ## show effect of tz argument anytime("2001-02-03 04:05:06") ## adjust parsed time to given TZ argument anytime("2001-02-03 04:05:06", tz="America/Los_Angeles") ## somewhat equvalent base R functionality format(anytime("2001-02-03 04:05:06"), tz="America/Los_Angeles")
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