How can i annotate with arrows the maximum and the minimum of ggplot in R?

i have a data frame with dates and values :

n = 1000
date = seq(as.Date("2022/1/1"), by = "day", length.out = n)
value = rnorm(n,0,1)
df = tibble(date,value);df

how can i ggplot this data frame and to plot in the geom_line or geom_point two arrows pointing the maximum value and the minimum value of the value variable ?

ggplot(data =df, aes(x = date,y=value)) + 
  geom_point()


ggplot(data =df, aes(x = date,y=value)) + 
  geom_line()

Any help ?

>Solution :

It’s easiest to create a dataframe of the data for the annotations and then add it to the plot.

Here I make maxmin_df, which contains the details of the maximum and minimum values, and then add a geom_segment() to add them to the ggplot().

You’ll need to decide on the look of the line and arrows.

max_df <- tibble(y = max(df$value), 
              yend = y, 
              x = df$date[which(df$value == y)] + lubridate::days(5),
              xend = x + lubridate::days(50))

minmax_df <- bind_rows(max_df,
                       c(tibble(y = min(df$value), 
                                yend = y, 
                                x = df$date[which(df$value == y)] + lubridate::days(5),
                                xend = x + lubridate::days(50))
                         )
                      )


ggplot(data = df, aes(x = date,y=value)) + 
  geom_point() +
  geom_segment(data = minmax_df, aes(x = xend, xend = x, y = y, yend = yend), colour = "red", arrow = arrow())