ggplot2 specify a secondary axis for both value and date/datetime

Question

I am trying to produce a ggplot graph where I can compare two time periods without indexing the data. So, that I get one time-window running along the x-axis at the bottom and one along the x-axis at the top, kinda like the the example from the tidyverse manual page (see graph at bottom of linked page).

However I would like to have dual axis on the y-axis too, something like this (made this by copy-pasiting using the code below),

economics_long %>% filter(variable== "pce" & date  > "2008-01-01" & date < "2010-01-01") %>% 
  ggplot(aes(date, value01, colour = variable)) + geom_line()

economics_long %>% filter(variable== "pce" & date  > "1990-01-01" & date < "1992-01-01") %>% 
  ggplot(aes(date, value01, colour = variable)) + geom_line()

I imagine I would need to use bind_rows() to cut the two time periods out and put them on top and maybe make a new variables like variable with two options, like time-window 1 and time-window 2, however I wanted to ask here before I start manually build something crazy. Maybe others have done something simular?

I have made some first steps, like,

tw01 <- economics_long %>% 
filter(variable== "pce" & date  > "2008-01-01" & date < "2010-01-01")
tw02 <- economics_long %>% 
filter(variable== "pce" & date  > "1990-01-01" & date < "1992-01-01")

tw02$date <- tw01$date
tw <- bind_rows(tw01, tw02, .id = "time_window")
tw %>% ggplot(aes(date, value01, colour = time_window)) + geom_line()

Answer 1

Maybe this is what you are looking for:

1. For the date transformation I make use of lubridate::years. Addtionally for the transformation inside sec_axis I to wrap into hms::hms as I otherwise got an error.
2. As I personally find secondary axes always a bit confusing, expecially with both a secondary x and y axis I colored both the x and y labels according to the color of the lines. If you don't like that you can simply drop the theme() adjustemnts.

library(ggplot2)
library(dplyr)

tw1_START <- "2008-01-01"; tw1_END <- "2010-01-01"
tw2_START <- "1990-01-01"; tw2_END <- "1992-01-01"
s_factor <- .52

Intv <- interval(ymd(tw2_START), ymd(tw1_START))
IntvM <-  time_length(Intv, "month") # time_length(YrDis , "year")


tw01 <- economics_long %>% 
  filter(variable== "pce" & date  > tw1_START  & date < tw1_END )

tw02 <- economics_long %>% 
  filter(variable== "pce" & date  > tw2_START  & date < tw2_END) %>% 
  mutate(date = date +  hms::hms(months(IntvM))) %>% 
  mutate(value01 = value01 + s_factor)


tw <- bind_rows(tw01, tw02, .id = "time_window")
tw %>% 
  ggplot(aes(date, value01, colour = time_window)) + 
  geom_line() + 
  scale_x_date(sec.axis = sec_axis(~ . -hms::hms(months(IntvM))))  + 
  scale_y_continuous(sec.axis = sec_axis(~ . - s_factor), position = "right") +
  theme(axis.text.x.top = element_text(color = scales::hue_pal()(2)[2]),
        axis.text.x.bottom = element_text(color = scales::hue_pal()(2)[1]),
        axis.text.y.right = element_text(color = scales::hue_pal()(2)[1]),
        axis.text.y.left = element_text(color = scales::hue_pal()(2)[2]))