Change an object to a period.
as.period changes Interval, Duration, difftime and numeric class objects to Period class objects with the specified units.
as.period(x, unit, ...)
- an interval, difftime, or numeric object
- A character string that specifies which time units to build period in. unit is only implemented for the as.period.numeric method and the as.period.interval method. For as.period.interval, as.period will convert intervals to units no larger than th
- additional arguments to pass to as.period
Users must specify which time units to measure the period
in. The exact length of each time unit in a period will
depend on when it occurs. See
new_period. The choice of units is not
trivial; units that are normally equal may differ in
length depending on when the time period occurs. For
example, when a leap second occurs one minute is longer
than 60 seconds.
Because periods do not have a fixed length, they can not
be accurately converted to and from Duration objects.
Duration objects measure time spans in exact numbers of
Duration-class. Hence, a one
to one mapping does not exist between durations and
periods. When used with a Duration object, as.period
provides an inexact estimate; the duration is broken into
time units based on the most common lengths of time
units, in seconds. Because the length of months are
particularly variable, a period with a months unit can
not be coerced from a duration object. For an exact
transformation, first transform the duration to an
Coercing an interval to a period may cause surprising behavior if you request periods with small units. A leap year is 366 days long, but one year long. Such an interval will convert to 366 days when unit is set to days and 1 year when unit is set to years. Adding 366 days to a date will often give a different result than adding one year. Daylight savings is the one exception where this does not apply. Interval lengths are calculated on the UTC timeline, which does not use daylight savings. Hence, periods converted with seconds or minutes will not reflect the actual variation in seconds and minutes that occurs due to daylight savings. These periods will show the "naive" change in seconds and minutes that is suggested by the differences in clock time. See the examples below.
as.period.difftime and as.period.duration display the
message "estimate only: convert difftimes (or duration)
to intervals for accuracy" by default. You can turn this
message off by setting the global
lubridate.verbose option to FALSE with
options(lubridate.verbose = FALSE).
- a period object
span <- new_interval(as.POSIXct("2009-01-01"), as.POSIXct("2010-02-02 01:01:01")) #interval # 2009-01-01 CST--2010-02-02 01:01:01 CST as.period(span) # "1y 1m 1d 1H 1M 1S" as.period(span, units = "day") "397d 1H 1M 1S" leap <- new_interval(ymd("2016-01-01"), ymd("2017-01-01")) # 2016-01-01 UTC--2017-01-01 UTC as.period(leap, unit = "days") # "366d 0H 0M 0S" as.period(leap, unit = "years") # "1y 0m 0d 0H 0M 0S" dst <- new_interval(ymd("2016-11-06", tz = "America/Chicago"), ymd("2016-11-07", tz = "America/Chicago")) # 2016-11-06 CDT--2016-11-07 CST # as.period(dst, unit = "seconds") # "86400S" as.period(dst, unit = "hours") # "24H 0M 0S"