Waiting + saving intermediary results in order to be able to re-launch if script stopped

get_followers.R

get_followers_and_wait <- function(user){
  # don't re-query the same data twice
  exists <- paste0("followers", user, ".RData") %in% dir("data/2017-06-03-twitter")
  if(exists){
    # if it already exists use it
    load(paste0("data/2017-06-03-twitter/followers", user, ".RData"))
  }else{
    # otherwise query after checking the rate limit
    rates <- rtweet::rate_limit(token = rtweet::get_tokens(),
                              query = "followers/ids")
  if(rates$remaining == 0){
    try_sleeping <- try(Sys.sleep(as.numeric(rates$reset)*60), 
                        silent = TRUE)
    if(methods::is(try_sleeping, "try-error")){
      Sys.sleep(15*60)
    }
    
  }
  followers <- rtweet::get_followers(user = user)
  followers <- dplyr::mutate_(followers, followed_person = ~user)
  save(followers, file = paste0("data/2017-06-03-twitter/followers", user, ".RData"))
  }
  return(followers)
}

followers_followers <- purrr::map_df(followers$user_id,
                                     get_followers_and_wait)