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Round, floor and ceiling methods for date-time objects

Source: R/round.r
round_date.Rd

round_date() takes a date-time object and time unit, and rounds it to the nearest value of the specified time unit. For rounding date-times which are exactly halfway between two consecutive units, the convention is to round up. Note that this is in line with the behavior of R's base::round.POSIXt() function but does not follow the convention of the base base::round() function which "rounds to the even digit", as per IEC 60559.

Rounding to the nearest unit or multiple of a unit is supported. All meaningful specifications in the English language are supported - secs, min, mins, 2 minutes, 3 years etc.

Rounding to fractional seconds is also supported. Please note that rounding to fractions smaller than 1 second can lead to large precision errors due to the floating point representation of the POSIXct objects. See examples.

floor_date() takes a date-time object and rounds it down to the nearest boundary of the specified time unit.

ceiling_date() takes a date-time object and rounds it up to the nearest boundary of the specified time unit.

Usage

round_date(
  x,
  unit = "second",
  week_start = getOption("lubridate.week.start", 7)
)

floor_date(
  x,
  unit = "seconds",
  week_start = getOption("lubridate.week.start", 7)
)

ceiling_date(
  x,
  unit = "seconds",
  change_on_boundary = NULL,
  week_start = getOption("lubridate.week.start", 7)
)

Arguments

x

a vector of date-time objects

unit

a string, Period object or a date-time object. When a singleton string, it specifies a time unit or a multiple of a unit to be rounded to. Valid base units are second, minute, hour, day, week, month, bimonth, quarter, season, halfyear and year. Arbitrary unique English abbreviations as in the period() constructor are allowed. Rounding to multiples of units (except weeks) is supported. When unit is a Period object, units of the period objects are used. This is equivalent to converting the period object to its string representation and passing as unit argument.

When unit is a date-time object rounding is done to the nearest of the elements in unit. If range of unit vector does not cover the range of x ceiling_date() and floor_date() round to the max(x) and min(x) for elements that fall outside of range(unit).

week_start

week start day (Default is 7, Sunday. Set lubridate.week.start to override). Full or abbreviated names of the days of the week can be in English or as provided by the current locale.

change_on_boundary

if this is NULL (the default), instants on the boundary remain unchanged, but Date objects are rounded up to the next boundary. If this is TRUE, instants on the boundary are rounded up to the next boundary. If this is FALSE, nothing on the boundary is rounded up at all. This was the default for lubridate prior to v1.6.0. See section Rounding Up Date Objects below for more details.

Value

When unit is a string, return a Date object if x is a Date and unit is larger or equal than "day", otherwise a POSIXct object. When unit is a date-time object, return a date-time object of the same class and same time zone as unit.

Details

In lubridate, functions that round date-time objects try to preserve the class of the input object whenever possible. This is done by first rounding to an instant, and then converting to the original class as per usual R conventions.

Rounding Up Date Objects

By default, rounding up Date objects follows 3 steps:

  1. Convert to an instant representing lower bound of the Date: 2000-01-01 --> 2000-01-01 00:00:00

  2. Round up to the next closest rounding unit boundary. For example, if the rounding unit is month then next closest boundary of 2000-01-01 is 2000-02-01 00:00:00.

    The motivation for this is that the "partial" 2000-01-01 is conceptually an interval (2000-01-01 00:00:00 -- 2000-01-02 00:00:00) and the day hasn't started clocking yet at the exact boundary 00:00:00. Thus, it seems wrong to round a day to its lower boundary.

    Behavior on the boundary can be changed by setting change_on_boundary to TRUE or FALSE.

  3. If the rounding unit is smaller than a day, return the instant from step 2 (POSIXct), otherwise convert to and return a Date object.

See also

base::round()

Examples


## print fractional seconds
options(digits.secs = 6)

x <- ymd_hms("2009-08-03 12:01:59.23")
round_date(x, ".5s")
#> [1] "2009-08-03 12:01:59 UTC"
round_date(x, "sec")
#> [1] "2009-08-03 12:01:59 UTC"
round_date(x, "second")
#> [1] "2009-08-03 12:01:59 UTC"
round_date(x, "minute")
#> [1] "2009-08-03 12:02:00 UTC"
round_date(x, "5 mins")
#> [1] "2009-08-03 12:00:00 UTC"
round_date(x, "hour")
#> [1] "2009-08-03 12:00:00 UTC"
round_date(x, "2 hours")
#> [1] "2009-08-03 12:00:00 UTC"
round_date(x, "day")
#> [1] "2009-08-04 UTC"
round_date(x, "week")
#> [1] "2009-08-02 UTC"
round_date(x, "month")
#> [1] "2009-08-01 UTC"
round_date(x, "bimonth")
#> [1] "2009-09-01 UTC"
round_date(x, "quarter") == round_date(x, "3 months")
#> [1] TRUE
round_date(x, "halfyear")
#> [1] "2009-07-01 UTC"
round_date(x, "year")
#> [1] "2010-01-01 UTC"

x <- ymd_hms("2009-08-03 12:01:59.23")
floor_date(x, ".1s")
#> [1] "2009-08-03 12:01:59.2 UTC"
floor_date(x, "second")
#> [1] "2009-08-03 12:01:59 UTC"
floor_date(x, "minute")
#> [1] "2009-08-03 12:01:00 UTC"
floor_date(x, "hour")
#> [1] "2009-08-03 12:00:00 UTC"
floor_date(x, "day")
#> [1] "2009-08-03 UTC"
floor_date(x, "week")
#> [1] "2009-08-02 UTC"
floor_date(x, "month")
#> [1] "2009-08-01 UTC"
floor_date(x, "bimonth")
#> [1] "2009-07-01 UTC"
floor_date(x, "quarter")
#> [1] "2009-07-01 UTC"
floor_date(x, "season")
#> [1] "2009-06-01 UTC"
floor_date(x, "halfyear")
#> [1] "2009-07-01 UTC"
floor_date(x, "year")
#> [1] "2009-01-01 UTC"

x <- ymd_hms("2009-08-03 12:01:59.23")
ceiling_date(x, ".1 sec") # imprecise representation at 0.1 sec !!!
#> [1] "2009-08-03 12:01:59.2 UTC"
ceiling_date(x, "second")
#> [1] "2009-08-03 12:02:00 UTC"
ceiling_date(x, "minute")
#> [1] "2009-08-03 12:02:00 UTC"
ceiling_date(x, "5 mins")
#> [1] "2009-08-03 12:05:00 UTC"
ceiling_date(x, "hour")
#> [1] "2009-08-03 13:00:00 UTC"
ceiling_date(x, "day")
#> [1] "2009-08-04 UTC"
ceiling_date(x, "week")
#> [1] "2009-08-09 UTC"
ceiling_date(x, "month")
#> [1] "2009-09-01 UTC"
ceiling_date(x, "bimonth") == ceiling_date(x, "2 months")
#> [1] TRUE
ceiling_date(x, "quarter")
#> [1] "2009-10-01 UTC"
ceiling_date(x, "season")
#> [1] "2009-09-01 UTC"
ceiling_date(x, "halfyear")
#> [1] "2010-01-01 UTC"
ceiling_date(x, "year")
#> [1] "2010-01-01 UTC"

## Period unit argument
floor_date(x, days(2))
#> [1] "2009-08-03 UTC"
floor_date(x, years(1))
#> [1] "2009-01-01 UTC"

## As of R 3.4.2 POSIXct printing of fractional numbers is wrong
as.POSIXct("2009-08-03 12:01:59.3") ## -> "2009-08-03 12:01:59.2 CEST"
#> [1] "2009-08-03 12:01:59.2 UTC"
ceiling_date(x, ".1 sec") ## -> "2009-08-03 12:01:59.2 CEST"
#> [1] "2009-08-03 12:01:59.2 UTC"

## behaviour of `change_on_boundary`
## As per default behaviour `NULL`, instants on the boundary remain the
## same but dates are rounded up
ceiling_date(ymd_hms("2000-01-01 00:00:00"), "month")
#> [1] "2000-01-01 UTC"
ceiling_date(ymd("2000-01-01"), "month")
#> [1] "2000-02-01"

## If `TRUE`, both instants and dates on the boundary are rounded up
ceiling_date(ymd_hms("2000-01-01 00:00:00"), "month", change_on_boundary = TRUE)
#> [1] "2000-02-01 UTC"
ceiling_date(ymd("2000-01-01"), "month")
#> [1] "2000-02-01"

## If `FALSE`, both instants and dates on the boundary remain the same
ceiling_date(ymd_hms("2000-01-01 00:00:00"), "month", change_on_boundary = FALSE)
#> [1] "2000-01-01 UTC"
ceiling_date(ymd("2000-01-01"), "month")
#> [1] "2000-02-01"

x <- ymd_hms("2000-01-01 00:00:00")
ceiling_date(x, "month")
#> [1] "2000-01-01 UTC"
ceiling_date(x, "month", change_on_boundary = TRUE)
#> [1] "2000-02-01 UTC"

## For Date objects first day of the month is not on the
## "boundary". change_on_boundary applies to instants only.
x <- ymd("2000-01-01")
ceiling_date(x, "month")
#> [1] "2000-02-01"
ceiling_date(x, "month", change_on_boundary = TRUE)
#> [1] "2000-02-01"