Find the Start of an Activity Day — acti_day

This is a custom-day-boundary alternative to lubridate::floor_date() with unit = "day". Use floor_date() when days begin at midnight; use acti_day_start() when a recording day begins at a different time, such as 04:00.

Usage

acti_day_start(time, day_start = hms::hms(0), timezone = NULL)

Arguments

time: A POSIXt vector.
day_start: An hms or HH:MM[:SS] day boundary.
timezone: Optional Olson timezone used to define the day boundary.

Value

A POSIXct vector.

Note

Activity studies often use a non-midnight boundary (for example, 04:00) so nocturnal behavior is assigned to the preceding activity day.

Examples

time = as.POSIXct(c("2020-01-01 03:00:00", "2020-01-01 05:00:00"), tz = "UTC")

# With a midnight boundary, this agrees with floor_date().
acti_day_start(time)
#> [1] "2020-01-01 UTC" "2020-01-01 UTC"
lubridate::floor_date(time, unit = "day")
#> [1] "2020-01-01 UTC" "2020-01-01 UTC"

# With a 04:00 boundary, 03:00 belongs to the preceding activity day.
acti_day_start(time, day_start = "04:00")
#> [1] "2019-12-31 04:00:00 UTC" "2020-01-01 04:00:00 UTC"