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

## 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"
```