label ggplot中每组的最小值和最大值如何？

Question

I have a dataset that counts number of posts per month per year. Looks like that:

   monthdate   year     n
   <date>     <dbl> <int>
 1 2020-01-01  2001   133
 2 2020-01-01  2002   129
 3 2020-01-01  2003   149
 4 2020-01-01  2004    96
 5 2020-01-01  2005    94
 6 2020-01-01  2006   109
 7 2020-01-01  2007   158
 8 2020-01-01  2008   138
 9 2020-01-01  2009    83

( monthdate as a date is needed only for rendering month names in ggplot).

So the resulting plot is generated like that:

posts %>% mutate(monthdate = as.Date(paste("2020", month, '01', sep = "-"))) %>%
  group_by(monthdate, year) %>% summarise(n = n()) %>%
  ggplot(aes(x = monthdate, y = n)) +
  geom_point(, stat = 'identity') +
  geom_smooth(method = "loess") +
  scale_x_date(date_breaks = "1 month", date_labels = "%b") 

and looks like that:

I want to give year labels for topmost and bottom most outliers, so for each month it can be seen which year produced the least and the most posts per month. What is the efficient way to do it?

Answer 1

Ok, I found the solution. Pretty simple:

posts %>% mutate(monthdate = as.Date(paste("2020", month, '01', sep = "-"))) %>%
  group_by(monthdate, year) %>% summarise(n = n()) %>% group_by(monthdate) %>% mutate(lab=case_when(n==max(n)|n==min(n)~year))%>%
  ggplot(aes(x = monthdate, y = n)) +
  geom_point(, stat = 'identity') +
  geom_smooth(method = "loess") +
  scale_x_date(date_breaks = "1 month", date_labels = "%b") +
  xlab('Month')+
  ylab('Number of posts')+ geom_text(aes(label=lab))

and the resulting plot is: