Function for turning Date into school year string

date_to_sy.R

## Date to SY function
## Year of 2nd argument does not matter
## Turns 2015-10-02 into "2015-16", and 2016-04-05 into "2015-16", with cutoff day = 2010-07-01
date_to_sy <- function(date_var, last_day_of_sy){
  if(!(is.Date(date_var) & is.Date(last_day_of_sy))){stop("`date_var` and `last_day_of_sy` must both be class Date")}
  cutoff_day <- day(last_day_of_sy)
  cutoff_month <- month(last_day_of_sy)
  case_when(
    is.na(date_var) ~ as.character(NA),
    month(date_var) > cutoff_month ~ paste0(year(date_var), " - ", year(date_var) + 1), # if past cutoff, X - X+!
    month(date_var) == cutoff_month & day(date_var) > cutoff_day ~ paste0(year(date_var), " - ", year(date_var) + 1), # past cutoff
    TRUE ~  paste0(year(date_var) - 1, " - ", year(date_var)) # prior to cutoff = X-1 to X
  )
}