CODEWITHSUNDEEP
rdatetimelubridate
Disou
Disou

Reputation: 23

Floor datetime with custom start time (lubridate)

Is there a way to floor dates using a custom start time instead of the earliest possible time?

For example, flooring hours in a day into 2 12-hour intervals starting at 8am and 8pm rather than 12am and 12pm.

Example:

x <- ymd_hms("2009-08-03 21:00:00")
y <- ymd_hms("2009-08-03 09:00:00")
floor_date(x, '12 hours')
floor_date(y, '12 hours')

# default lubridate output:
[1] "2009-08-03 12:00:00 UTC"
[1] "2009-08-03 UTC"

# what i would like to have:
[1] "2009-08-03 20:00:00 UTC"
[1] "2009-08-03 08:00:00 UTC"

Upvotes: 0

Views: 288

Answers (1)

jay.sf
jay.sf

Reputation: 73272

You could program a small switch (without lubridate, though).

FUN <- function(x) {
  s <- switch(which.min(abs(mapply(`-`, c(8, 20), as.numeric(substr(x, 12, 13))))), 
              "08:00:00", "20:00:00")
  as.POSIXct(paste(as.Date(x), s))
}
FUN("2009-08-03 21:00:00")
# [1] "2009-08-03 20:00:00 CEST"

FUN("2009-08-03 09:00:00")
# [1] "2009-08-03 08:00:00 CEST"

Upvotes: 1

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