Replace time zone to create new date-time

Source: R/time-zones.r

force_tz returns the date-time that has the same clock time as input time, but in the new time zone. force_tzs is the parallel version of force_tz, meaning that every element from time argument is matched with the corresponding time zone in tzones argument.

force_tz(time, tzone = "", ...)

# Default S3 method
force_tz(time, tzone = "", roll_dst = c("NA", "post"), roll = NULL, ...)

force_tzs(
  time,
  tzones,
  tzone_out = "UTC",
  roll_dst = c("NA", "post"),
  roll = NULL
)

Arguments

time

a POSIXct, POSIXlt, Date, chron date-time object, or a data.frame object. When a data.frame all POSIXt elements of a data.frame are processed with force_tz() and new data.frame is returned.

tzone

a character string containing the time zone to convert to. R must recognize the name contained in the string as a time zone on your system.

...

Parameters passed to other methods.

roll_dst

is a string vector of length one or two. When two values are supplied they specify how to roll date-times when they fall into "skipped" and "repeated" DST transitions respectively. A single value is replicated to the length of two. Possible values are:

* `pre` - Use the time before the transition boundary.
* `boundary` - Use the time exactly at the boundary transition.
* `post` - Use the time after the boundary transition.
* `xfirst` - crossed-first: First time which occurred when crossing the
   boundary. For addition with positive units pre interval is crossed first and
   post interval last. With negative units post interval is crossed first, pre -
   last. For subtraction the logic is reversed.
* `xlast` - crossed-last.
* `NA` - Produce NAs when the resulting time falls inside the problematic interval.

For example `roll_dst = c("NA", "pre") indicates that for skipped intervals return NA and for repeated times return the earlier time.

When multiple units are supplied the meaning of "negative period" is determined by the largest unit. For example time_add(t, days = -1, hours = 2, roll_dst = "xfirst") would operate as if with negative period, thus crossing the boundary from the "post" to "pre" side and "xfirst" and hence resolving to "post" time. As this might result in confusing behavior. See examples.

"xfirst" and "xlast" make sense for addition and subtraction only. An error is raised if an attempt is made to use them with other functions.

roll

deprecated, same as roll_dst parameter.

tzones

character vector of timezones to be "enforced" on time time stamps. If time and tzones lengths differ, the smaller one is recycled in accordance with usual R conventions.

tzone_out

timezone of the returned date-time vector (for force_tzs).

Value

a POSIXct object in the updated time zone

Details

Although the new date-time has the same clock time (e.g. the same values in the year, month, days, etc. elements) it is a different moment of time than the input date-time.

As R date-time vectors cannot hold elements with non-uniform time zones, force_tzs returns a vector with time zone tzone_out, UTC by default.

Examples

x <- ymd_hms("2009-08-07 00:00:01", tz = "America/New_York")
force_tz(x, "UTC")
#> [1] "2009-08-07 00:00:01 UTC"
force_tz(x, "Europe/Amsterdam")
#> [1] "2009-08-07 00:00:01 CEST"

## DST skip:
y <- ymd_hms("2010-03-14 02:05:05 UTC")
force_tz(y, "America/New_York", roll_dst = "NA")
#> [1] NA
force_tz(y, "America/New_York", roll_dst = "pre")
#> [1] "2010-03-14 01:05:05 EST"
force_tz(y, "America/New_York", roll_dst = "boundary")
#> [1] "2010-03-14 03:00:00 EDT"
force_tz(y, "America/New_York", roll_dst = "post")
#> [1] "2010-03-14 03:05:05 EDT"

## DST repeat
y <- ymd_hms("2014-11-02 01:35:00", tz = "UTC")
force_tz(y, "America/New_York", roll_dst = "NA")
#> [1] NA
force_tz(y, "America/New_York", roll_dst = "pre")
#> [1] "2014-11-02 01:35:00 EDT"
force_tz(y, "America/New_York", roll_dst = "boundary")
#> [1] "2014-11-02 01:00:00 EST"
force_tz(y, "America/New_York", roll_dst = "post")
#> [1] "2014-11-02 01:35:00 EST"

## DST skipped and repeated
y <- ymd_hms("2010-03-14 02:05:05 UTC", "2014-11-02 01:35:00", tz = "UTC")
force_tz(y, "America/New_York", roll_dst = c("NA", "pre"))
#> [1] NA                        "2014-11-02 01:35:00 EDT"
force_tz(y, "America/New_York", roll_dst = c("boundary", "post"))
#> [1] "2010-03-14 03:00:00 EDT" "2014-11-02 01:35:00 EST"

## Heterogeneous time-zones:

x <- ymd_hms(c("2009-08-07 00:00:01", "2009-08-07 01:02:03"))
force_tzs(x, tzones = c("America/New_York", "Europe/Amsterdam"))
#> [1] "2009-08-07 04:00:01 UTC" "2009-08-06 23:02:03 UTC"
force_tzs(x, tzones = c("America/New_York", "Europe/Amsterdam"), tzone_out = "America/New_York")
#> [1] "2009-08-07 00:00:01 EDT" "2009-08-06 19:02:03 EDT"

x <- ymd_hms("2009-08-07 00:00:01")
force_tzs(x, tzones = c("America/New_York", "Europe/Amsterdam"))
#> [1] "2009-08-07 04:00:01 UTC" "2009-08-06 22:00:01 UTC"