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Group date-time components

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

This is a POSIXct/POSIXlt method for the date_group() generic.

date_group() groups by a single component of a date-time, such as month of the year, day of the month, or hour of the day.

If you need to group by more complex components, like ISO weeks, or quarters, convert to a calendar type that contains the component you are interested in grouping by.

Usage

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

Arguments

x

[POSIXct / POSIXlt]

A date-time vector.

precision

[character(1)]

One of:

  • "year"

  • "month"

  • "day"

  • "hour"

  • "minute"

  • "second"

...

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.

invalid

[character(1) / NULL]

One of the following invalid date resolution strategies:

  • "previous": The previous valid instant in time.

  • "previous-day": The previous valid day in time, keeping the time of day.

  • "next": The next valid instant in time.

  • "next-day": The next valid day in time, keeping the time of day.

  • "overflow": Overflow by the number of days that the input is invalid by. Time of day is dropped.

  • "overflow-day": Overflow by the number of days that the input is invalid by. Time of day is kept.

  • "NA": Replace invalid dates with NA.

  • "error": Error on invalid dates.

Using either "previous" or "next" is generally recommended, as these two strategies maintain the relative ordering between elements of the input.

If NULL, defaults to "error".

If getOption("clock.strict") is TRUE, invalid must be supplied and cannot be NULL. This is a convenient way to make production code robust to invalid dates.

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, grouped at precision.

Examples

x <- as.POSIXct("2019-01-01", "America/New_York")
x <- add_days(x, -3:5)

# Group by 2 days of the current month.
# Note that this resets at the beginning of the month, creating day groups
# of [29, 30] [31] [01, 02] [03, 04].
date_group(x, "day", n = 2)
#> [1] "2018-12-29 EST" "2018-12-29 EST" "2018-12-31 EST" "2019-01-01 EST"
#> [5] "2019-01-01 EST" "2019-01-03 EST" "2019-01-03 EST" "2019-01-05 EST"
#> [9] "2019-01-05 EST"

# Group by month
date_group(x, "month")
#> [1] "2018-12-01 EST" "2018-12-01 EST" "2018-12-01 EST" "2019-01-01 EST"
#> [5] "2019-01-01 EST" "2019-01-01 EST" "2019-01-01 EST" "2019-01-01 EST"
#> [9] "2019-01-01 EST"

# Group by hour of the day
y <- as.POSIXct("2019-12-30", "America/New_York")
y <- add_hours(y, 0:12)
y
#>  [1] "2019-12-30 00:00:00 EST" "2019-12-30 01:00:00 EST"
#>  [3] "2019-12-30 02:00:00 EST" "2019-12-30 03:00:00 EST"
#>  [5] "2019-12-30 04:00:00 EST" "2019-12-30 05:00:00 EST"
#>  [7] "2019-12-30 06:00:00 EST" "2019-12-30 07:00:00 EST"
#>  [9] "2019-12-30 08:00:00 EST" "2019-12-30 09:00:00 EST"
#> [11] "2019-12-30 10:00:00 EST" "2019-12-30 11:00:00 EST"
#> [13] "2019-12-30 12:00:00 EST"

date_group(y, "hour", n = 3)
#>  [1] "2019-12-30 00:00:00 EST" "2019-12-30 00:00:00 EST"
#>  [3] "2019-12-30 00:00:00 EST" "2019-12-30 03:00:00 EST"
#>  [5] "2019-12-30 03:00:00 EST" "2019-12-30 03:00:00 EST"
#>  [7] "2019-12-30 06:00:00 EST" "2019-12-30 06:00:00 EST"
#>  [9] "2019-12-30 06:00:00 EST" "2019-12-30 09:00:00 EST"
#> [11] "2019-12-30 09:00:00 EST" "2019-12-30 09:00:00 EST"
#> [13] "2019-12-30 12:00:00 EST"