有趣的是，如果我们查看计划起飞时间，就看不到如此明显的模式：

sched_dep <- flights_dt %>% mutate(minute = minute(sched_dep_time)) %>% group_by(minute) %>% summarize( avg_delay = mean(arr_delay, na.rm = TRUE), n = n()) ggplot(sched_dep, aes(minute, avg_delay)) + geom_line()