Perturb start and end times keeping duration within same "bins"

perturb_start_end_los

perturb_start_end_los <- function(
  df,
  max_shift_size_hours = 24,
  min_binsize_mins = 15
  ){

  df <- df %>%
    dplyr::mutate(los = spell_end - spell_start,
                  binstart = 15*floor(as.numeric(los, units = "mins")/15),
                  binend = 15*(floor(as.numeric(los, units = "mins")/15) + 1),
                  start_shift = as.difftime(runif(n = nrow(.),
                                      min = -max_shift_size_hours,
                                      max = max_shift_size_hours),
                                      units = "hours"),
                  spell_start_new = spell_start + start_shift,
                  initial_ed_end_datetime_new = initial_ed_end_datetime + start_shift) %>%
    dplyr::rowwise() %>%
    dplyr::mutate(los_new = as.difftime(round(runif(1L,
                                              min = binstart + 1,
                                              max = binend - 1)),
                                        units = "mins")) %>%
    dplyr::ungroup() %>%
    dplyr::mutate(spell_end_new = spell_start_new + los_new)

  df <- df %>%
    dplyr::select(-spell_start, -spell_end, -initial_ed_end_datetime, -los,
                  -binstart, -binend, -start_shift, -los_new) %>%
    dplyr::rename(spell_start = spell_start_new, spell_end = spell_end_new,
                  initial_ed_end_datetime = initial_ed_end_datetime_new)

  return(df)
}