Extract one year from a period of time involving two years in R

Question

This question already has answers here: question from:https://stackoverflow.com/questions/65871817/extract-one-year-from-a-period-of-time-involving-two-years-in-r

Answer 1

You could extract the actual year from first four substrings, then compare if it is smaller than all dates of the standardized year starting in the actual year. The standardized year we get from sequences with ISOdate.

standardized_year <- sapply(dat$events, function(x) {
  x <- as.POSIXct(x)
  y <- as.numeric(substr(x, 1, 4))
  ifelse(all(x < seq(ISOdate(y, 7, 1, 0), ISOdate(y + 1, 6, 30, 0), "day")), y - 1, y)
})
dat <- cbind(dat, standardized_year)
dat
#       events standardized_year
# 1 2018-02-02              2017
# 2 2010-05-24              2009
# 3 2019-12-30              2019
# 4 2020-07-01              2020