period: Create or parse period objects

Description

period() creates or parses a period object with the specified values.

Usage

period(num = NULL, units = "second", ...)
is.period(x)
seconds(x = 1)
minutes(x = 1)
hours(x = 1)
days(x = 1)
weeks(x = 1)
years(x = 1)
milliseconds(x = 1)
microseconds(x = 1)
nanoseconds(x = 1)
picoseconds(x = 1)
# S3 method for numeric
months(x, abbreviate)

Value

a period object

Arguments

num: a numeric or character vector. A character vector can specify periods in a convenient shorthand format or ISO 8601 specification. All unambiguous name units and abbreviations are supported, "m" stands for months, "M" for minutes unless ISO 8601 "P" modifier is present (see examples). Fractional units are supported but the fractional part is always converted to seconds.
units: a character vector that lists the type of units to be used. The units in units are matched to the values in num according to their order. When num is character, this argument is ignored.
...: a list of time units to be included in the period and their amounts. Seconds, minutes, hours, days, weeks, months, and years are supported. Normally only one of num or ... are present. If both are present, the periods are concatenated.
x: Any R object for is.periods and a numeric value of the number of units for elementary constructors. With the exception of seconds(), x must be an integer.
abbreviate: Ignored. For consistency with S3 generic in base namespace.

Details

Within a Period object, time units do not have a fixed length (except for seconds) until they are added to a date-time. The length of each time unit will depend on the date-time to which it is added. For example, a year that begins on 2009-01-01 will be 365 days long. A year that begins on 2012-01-01 will be 366 days long. When math is performed with a period object, each unit is applied separately. How the length of a period is distributed among its units is non-trivial. For example, when leap seconds occur 1 minute is longer than 60 seconds.

Periods track the change in the "clock time" between two date-times. They are measured in common time related units: years, months, days, hours, minutes, and seconds. Each unit except for seconds must be expressed in integer values.

Besides the main constructor and parser period(), period objects can also be created with the specialized functions years(), months(), weeks(), days(), hours(), minutes(), and seconds(). These objects can be added to and subtracted to date-times to create a user interface similar to object oriented programming.

Note: Arithmetic with periods can result in undefined behavior when non-existent dates are involved (such as February 29th in non-leap years). Please see Period for more details and %m+% and add_with_rollback() for alternative operations.

Examples

Run this code


### Separate period and units vectors

period(c(90, 5), c("second", "minute"))
#  "5M 90S"
period(-1, "days")
period(c(3, 1, 2, 13, 1), c("second", "minute", "hour", "day", "week"))
period(c(1, -60), c("hour", "minute"))
period(0, "second")

### Units as arguments

period (second = 90, minute = 5)
period(day = -1)
period(second = 3, minute = 1, hour = 2, day = 13, week = 1)
period(hour = 1, minute = -60)
period(second = 0)
period(c(1, -60), c("hour", "minute"), hour = c(1, 2), minute = c(3, 4))

### Lubridate style parsing

period("2M 1sec")
period("2hours 2minutes 1second")
period("2d 2H 2M 2S")
period("2days 2hours 2mins 2secs")
period("2 days, 2 hours, 2 mins, 2 secs")
# Missing numerals default to 1. Repeated units are added up.
duration("day day")

### ISO 8601 parsing

period("P10M23DT23H") # M stands for months
period("10DT10M") # M stands for minutes
period("P3Y6M4DT12H30M5S") # M for both minutes and months
period("P23DT60H 20min 100 sec") # mixing ISO and lubridate style parsing

### Comparison with characters (from v1.6.0)

duration("day 2 sec") > "day 1sec"

### Elementary Constructors

x <- ymd("2009-08-03")
x + days(1) + hours(6) + minutes(30)
x + days(100) - hours(8)

class(as.Date("2009-08-09") + days(1)) # retains Date class
as.Date("2009-08-09") + hours(12)
class(as.Date("2009-08-09") + hours(12))
# converts to POSIXt class to accomodate time units

years(1) - months(7)
c(1:3) * hours(1)
hours(1:3)

# sequencing
y <- ymd(090101) # "2009-01-01 CST"
y + months(0:11)

# compare DST handling to durations
boundary <- ymd_hms("2009-03-08 01:59:59", tz="America/Chicago")
boundary + days(1) # period
boundary + ddays(1) # duration
is.period(as.Date("2009-08-03")) # FALSE
is.period(period(months= 1, days = 15)) # TRUE