This is a Date method for the date_group() generic.

date_group() groups by a single component of a Date, such as month of the year, or day of the month.

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 Date
date_group(x, precision, ..., n = 1L, invalid = NULL)

## Arguments

x

[Date]

A date vector.

precision

[character(1)]

One of:

• "year"

• "month"

• "day"

...

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.

## Value

x, grouped at precision.

## Examples

x <- as.Date("2019-01-01") + -3:5
x
#> [1] "2018-12-29" "2018-12-30" "2018-12-31" "2019-01-01" "2019-01-02"
#> [6] "2019-01-03" "2019-01-04" "2019-01-05" "2019-01-06"

# 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" "2018-12-29" "2018-12-31" "2019-01-01" "2019-01-01"
#> [6] "2019-01-03" "2019-01-03" "2019-01-05" "2019-01-05"

# Group by month
date_group(x, "month")
#> [1] "2018-12-01" "2018-12-01" "2018-12-01" "2019-01-01" "2019-01-01"
#> [6] "2019-01-01" "2019-01-01" "2019-01-01" "2019-01-01"