as-zoned-time-Date {clock}

Convert to a zoned-time from a date

Description

This is a Date method for the as_zoned_time() generic.

clock assumes that Dates are naive date-time types. Like naive-times, they have a yet-to-be-specified time zone. This method allows you to specify that time zone, keeping the printed time. If possible, the time will be set to midnight (see Details for the rare case in which this is not possible).

Usage

## S3 method for class 'Date'
as_zoned_time(x, zone, ..., nonexistent = NULL, ambiguous = NULL)

Arguments

x

⁠[Date]⁠

A Date.

zone

⁠[character(1)]⁠

The zone to convert to.

...

These dots are for future extensions and must be empty.

nonexistent

⁠[character / NULL]⁠

One of the following nonexistent time resolution strategies, allowed to be either length 1, or the same length as the input:

• "roll-forward": The next valid instant in time.

• "roll-backward": The previous valid instant in time.

• "shift-forward": Shift the nonexistent time forward by the size of the daylight saving time gap.

• ⁠"shift-backward⁠: Shift the nonexistent time backward by the size of the daylight saving time gap.

• "NA": Replace nonexistent times with NA.

• "error": Error on nonexistent times.

Using either "roll-forward" or "roll-backward" is generally recommended over shifting, as these two strategies maintain the relative ordering between elements of the input.

If NULL, defaults to "error".

If getOption("clock.strict") is TRUE, nonexistent must be supplied and cannot be NULL. This is a convenient way to make production code robust to nonexistent times.

ambiguous

⁠[character / zoned_time / POSIXct / list(2) / NULL]⁠

One of the following ambiguous time resolution strategies, allowed to be either length 1, or the same length as the input:

• "earliest": Of the two possible times, choose the earliest one.

• "latest": Of the two possible times, choose the latest one.

• "NA": Replace ambiguous times with NA.

• "error": Error on ambiguous times.

Alternatively, ambiguous is allowed to be a zoned_time (or POSIXct) that is either length 1, or the same length as the input. If an ambiguous time is encountered, the zoned_time is consulted. If the zoned_time corresponds to a naive_time that is also ambiguous and uses the same daylight saving time transition point as the original ambiguous time, then the offset of the zoned_time is used to resolve the ambiguity. If the ambiguity cannot be resolved by consulting the zoned_time, then this method falls back to NULL.

Finally, ambiguous is allowed to be a list of size 2, where the first element of the list is a zoned_time (as described above), and the second element of the list is an ambiguous time resolution strategy to use when the ambiguous time cannot be resolved by consulting the zoned_time. Specifying a zoned_time on its own is identical to ⁠list(<zoned_time>, NULL)⁠.

If NULL, defaults to "error".

If getOption("clock.strict") is TRUE, ambiguous must be supplied and cannot be NULL. Additionally, ambiguous cannot be specified as a zoned_time on its own, as this implies NULL for ambiguous times that the zoned_time cannot resolve. Instead, it must be specified as a list alongside an ambiguous time resolution strategy as described above. This is a convenient way to make production code robust to ambiguous times.

Details

In the rare instance that the specified time zone does not contain a date-time at midnight due to daylight saving time, nonexistent can be used to resolve the issue. Similarly, if there are two possible midnight times due to a daylight saving time fallback, ambiguous can be used.

Value

A zoned-time.

Examples

x <- as.Date("2019-01-01")

# The resulting zoned-times have the same printed time, but are in
# different time zones
as_zoned_time(x, "UTC")
as_zoned_time(x, "America/New_York")

# Converting Date -> zoned-time is the same as naive-time -> zoned-time
x <- as_naive_time(year_month_day(2019, 1, 1))
as_zoned_time(x, "America/New_York")

# In Asia/Beirut, there was a DST gap from
# 2021-03-27 23:59:59 -> 2021-03-28 01:00:00,
# skipping the 0th hour entirely. This means there is no midnight value.
x <- as.Date("2021-03-28")
try(as_zoned_time(x, "Asia/Beirut"))

# To resolve this, set a `nonexistent` time resolution strategy
as_zoned_time(x, "Asia/Beirut", nonexistent = "roll-forward")