Round, floor and ceiling methods for date-time objects.

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Description

Rounding to the nearest unit or multiple of a unit are supported. All meaningfull specifications in English language are supported - secs, min, mins, 2 minutes, 3 years etc.
round_date takes a date-time object and rounds it to the nearest value of the specified time unit. For rounding date-times which is 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 round function which "rounds to the even digit" per IEC 60559.
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

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round_date(x, unit = "second")

floor_date(x, unit = "seconds")

ceiling_date(x, unit = "seconds", change_on_boundary = NULL)

Arguments

x

a vector of date-time objects

unit

a character string specifying the time unit or a multiple of a unit to be rounded to. Valid base units are second, minute, hour, day, week, month, bimonth, quarter, halfyear, or year. Arbitrary unique English abbreviations as in period constructor are also supported. Rounding to multiple of units (except weeks) is supported from v1.6.0.

change_on_boundary

If NULL (the default) don't change instants on the boundary (ceiling_date(ymd_hms('2000-01-01 00:00:00')) is 2000-01-01 00:00:00), but round up Date objects to the next boundary (ceiling_date(ymd("2000-01-01"), "month") is "2000-02-01"). When TRUE, instants on the boundary are rounded up to the next boundary. When FALSE, date-time on the boundary are never rounded up (this was the default for lubridate prior to v1.6.0. See section Rounding Up Date Objects below for more details.

Details

In lubridate rounding of a date-time objects tries to preserve the class of the input object whenever it is meaningful. This is done by first rounding to an instant and then converting to the original class by 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 boundary for 2000-01-01 will be 2000-02-01 00:00:00.

    The motivation for this behavior is that 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 up a day to its lower boundary.

  3. If rounding unit is smaller than a day, return the instant from step 2 above (POSIXct), otherwise return the Date immediately following that instant.

The behavior on the boundary in the second step above can be changed by setting change_on_boundary to a non-NULL value.

See Also

round

Examples

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x <- as.POSIXct("2009-08-03 12:01:59.23")
round_date(x, "second")
round_date(x, "minute")
round_date(x, "5 mins")
round_date(x, "hour")
round_date(x, "2 hours")
round_date(x, "day")
round_date(x, "week")
round_date(x, "month")
round_date(x, "bimonth")
round_date(x, "quarter") == round_date(x, "3 months")
round_date(x, "halfyear")
round_date(x, "year")

x <- as.POSIXct("2009-08-03 12:01:59.23")
floor_date(x, "second")
floor_date(x, "minute")
floor_date(x, "hour")
floor_date(x, "day")
floor_date(x, "week")
floor_date(x, "month")
floor_date(x, "bimonth")
floor_date(x, "quarter")
floor_date(x, "halfyear")
floor_date(x, "year")

x <- as.POSIXct("2009-08-03 12:01:59.23")
ceiling_date(x, "second")
ceiling_date(x, "minute")
ceiling_date(x, "5 mins")
ceiling_date(x, "hour")
ceiling_date(x, "day")
ceiling_date(x, "week")
ceiling_date(x, "month")
ceiling_date(x, "bimonth") == ceiling_date(x, "2 months")
ceiling_date(x, "quarter")
ceiling_date(x, "halfyear")
ceiling_date(x, "year")
x <- ymd("2000-01-01")
ceiling_date(x, "month")
ceiling_date(x, "month", change_on_boundary = TRUE)

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