Set upper and lower limits for geom_area() in ggplot2

Question

I plotted geom_line() and geom_hline() for date and fb columns in df:

df <- structure(list(date = c("2015-5-1", "2015-6-1", "2015-7-1", "2015-8-1", 
"2015-9-1", "2015-10-1", "2015-11-1", "2015-12-1", "2016-1-1", 
"2016-2-1", "2016-3-1", "2016-4-1", "2016-5-1", "2016-6-1", "2016-7-1", 
"2016-8-1", "2016-9-1", "2016-10-1"), fb = c(8.055790592, 8.032818097, 
8.005365822, 7.985498773, 7.959200396, 7.919847621, 7.877668588, 
7.835635821, 7.804472389, 7.788280201, 7.772438537, 7.750286446, 
7.720577645, 7.699622927, 7.679943452, 7.671596434, 7.678374461, 
7.677040934), ab = c(14.79734541, 14.66345424, 14.52954117, 14.39551705, 
14.2613928, 14.12742798, 13.99331597, 13.85911943, 13.7250579, 
13.59078964, 13.45659479, 13.32220287, 13.18777806, 13.05347518, 
12.91905494, 12.78450571, 12.65039408, 12.51588272)), class = "data.frame", row.names = c(NA, 
-18L))


df1 <- df %>% 
  mutate_at(vars(-date), funs(./100))
df1 %>% 
  ggplot(aes(x=as.POSIXct(date), y=fb)) + 
  geom_line(size=1, alpha=0.7, color='red') +
  # geom_area(fill='red', alpha=0.3, position = "identity") +
  geom_hline(yintercept=c(min(df1$fb), max(df1$fb)), linetype='solid', col='black')

I filled area using geom_area(fill='red', alpha=0.3, position = "identity"), but as you may notice, the area starting from df1$fb == 0 which generate a large futile areas (areas in the blue rectangle as shown in the figure below).

df1 %>% 
  ggplot(aes(x=as.POSIXct(date), y=fb)) + 
  geom_line(size=1, alpha=0.7, color='red') +
  geom_area(fill='red', alpha=0.3, position = "identity") +
  geom_hline(yintercept=c(min(df1$fb), max(df1$fb)), linetype='solid', col='black')

So my question is how could we only fill the underline area between minimum and maximum values of fb? Thanks for your help at advance.

Answer 1

geom_area is a special case of geom_ribbon which starts at 0. Use geom_ribbon and specify ymin and y:

df1 %>% 
  ggplot(aes(x=as.POSIXct(date), y=fb)) + 
  geom_line(size=1, alpha=0.7, color='red') +
  geom_ribbon(aes(ymin = min(fb), ymax = fb), fill = 'red', alpha=0.3, position = "identity") +
  geom_hline(yintercept=c(min(df1$fb), max(df1$fb)), linetype='solid', col='black')