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Rounding: date-time

Source: R/posixt.R
posixt-rounding.Rd

These are POSIXct/POSIXlt methods for the rounding generics.

  • date_floor() rounds a date-time down to a multiple of the specified precision.

  • date_ceiling() rounds a date-time up to a multiple of the specified precision.

  • date_round() rounds up or down depending on what is closer, rounding up on ties.

You can group by irregular periods such as "month" or "year" by using date_group().

Usage

# S3 method for class 'POSIXt'
date_floor(
  x,
  precision,
  ...,
  n = 1L,
  origin = NULL,
  nonexistent = NULL,
  ambiguous = x
)

# S3 method for class 'POSIXt'
date_ceiling(
  x,
  precision,
  ...,
  n = 1L,
  origin = NULL,
  nonexistent = NULL,
  ambiguous = x
)

# S3 method for class 'POSIXt'
date_round(
  x,
  precision,
  ...,
  n = 1L,
  origin = NULL,
  nonexistent = NULL,
  ambiguous = x
)

Arguments

x

[POSIXct / POSIXlt]

A date-time vector.

precision

[character(1)]

One of:

  • "week"

  • "day"

  • "hour"

  • "minute"

  • "second"

"week" is an alias for "day" with n * 7.

...

These dots are for future extensions and must be empty.

n

[positive integer(1)]

A single positive integer specifying a multiple of precision to use.

origin

[POSIXct(1) / POSIXlt(1) / NULL]

An origin to start counting from.

origin must have exactly the same time zone as x.

origin will be floored to precision. If information is lost when flooring, a warning will be thrown.

If NULL, defaults to midnight on 1970-01-01 in the time zone of x.

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.

Value

x rounded to the specified precision.

Details

When rounding by "week", remember that the origin determines the "week start". By default, 1970-01-01 is the implicit origin, which is a Thursday. If you would like to round by weeks with a different week start, just supply an origin on the weekday you are interested in.

Examples

x <- as.POSIXct("2019-03-31", "America/New_York")
x <- add_days(x, 0:5)

# Flooring by 2 days, note that this is not tied to the current month,
# and instead counts from the specified `origin`, so groups can cross
# the month boundary
date_floor(x, "day", n = 2)
#> [1] "2019-03-31 EDT" "2019-03-31 EDT" "2019-04-02 EDT" "2019-04-02 EDT"
#> [5] "2019-04-04 EDT" "2019-04-04 EDT"

# Compare to `date_group()`, which groups by the day of the month
date_group(x, "day", n = 2)
#> [1] "2019-03-31 EDT" "2019-04-01 EDT" "2019-04-01 EDT" "2019-04-03 EDT"
#> [5] "2019-04-03 EDT" "2019-04-05 EDT"

# Note that daylight saving time gaps can throw off rounding
x <- as.POSIXct("1970-04-26 01:59:59", "America/New_York") + c(0, 1)
x
#> [1] "1970-04-26 01:59:59 EST" "1970-04-26 03:00:00 EDT"

# Rounding is done in naive-time, which means that rounding by 2 hours
# will attempt to generate a time of 1970-04-26 02:00:00, which doesn't
# exist in this time zone
try(date_floor(x, "hour", n = 2))
#> Error in as_zoned_time(x, zone = tz, nonexistent = nonexistent, ambiguous = ambiguous) : 
#>   Nonexistent time due to daylight saving time at location 2.
#> ℹ Resolve nonexistent time issues by specifying the `nonexistent` argument.

# You can handle this by specifying a nonexistent time resolution strategy
date_floor(x, "hour", n = 2, nonexistent = "roll-forward")
#> [1] "1970-04-26 00:00:00 EST" "1970-04-26 03:00:00 EDT"