查看平均延误时间最长（按尾号识别）的飞机：

delays <- not_cancelled %>% group_by(tailnum) %>% summarize( delay = mean(arr_delay) ) ggplot(data = delays, mapping = aes(x = delay)) + geom_freqpoly(binwidth = 10)

哇，居然有一些飞机的平均延误达到 5 小时（300 分钟）！

实际情况其实更微妙一些。如果我们绘制航班数量与平均延误时间的散点图，可以获得更深入的了解：

delays <- not_cancelled %>% group_by(tailnum) %>% summarize( delay = mean(arr_delay, na.rm = TRUE), n = n() ) ggplot(data = delays, mapping = aes(x = n, y = delay)) + geom_point(alpha = 1/10)