Automatic way to highlight parts of a time series plot that have values higher than a certain threshold?

Question

I\'m looking for an automatic way of highlighting some portions of the plot that have Station2 values greater than a pre-defined threshold which is 0 in this case.

Answer 1

Something like:

library(dplyr)
dateRanges <- df %>% 
  mutate(Date2 = lead(Date)) %>% 
  filter(key == 'Station2', value > 0 | lead(value) > 0, Date2 - Date == 1)

gg1 +
  geom_rect(data = dateRanges, 
            aes(xmin = Date, xmax = Date2, ymin = -Inf, ymax = Inf), 
            inherit.aes = FALSE,
            color = NA,
            fill = 'grey20',
            alpha = 0.2)

It's easiest to just draw one rect for per day.