R ggplot - 用两个轴在同一 plot 中绘制具有子类别的多个变量

Question

I have this data:

date        area        people_tested    positive_cases positive
2021-12-09  Total       76282.0                402.0000 0.005300000
2021-12-10  Total       84023.0                389.0000 0.004600000
2021-12-09  Total_3da        NA                382.3333 0.004900000
2021-12-10  Total_3da        NA                377.6667 0.004933333
2021-12-09  Paris_3da   75257.4                      NA          NA
2021-12-10  Paris_3da   71553.6                      NA          NA

and I would like to create a plot with a line for each combination. For example:

1. Line 1 -> Total / people_tested
2. Line 2 -> Total / positive_cases
3. Line 3 -> Total / positive
4. Line 4 -> Total_3da / positive_cases
5. Line 5 -> Total_3da / positive
6. Line 6 -> Paris_3da / people_tested

I would also like for 'people_tested' & 'positive_cases' to be on the same axis and the 'positive' to be on a secondary axis.

One way I've thought about doing it is to created a new table with the following format but I was wondering if there is a more simple way to do it:

date        area                      value 
2021-12-09  Total_people_tested     76282.0                
2021-12-10  Total_people_tested     84023.0  
2021-12-09  Total_positive_cases      402.0
2021-12-10  Total_positive_cases      389.0
etc

Answer 1

Directly on ggplot2, I believe is not possible. One solution is combining a reshape step with facet_grid. Something like:

library(tidyr)

# reshaping to long form
df_tidy <- df %>%
    pivot_longer(cols = people_tested:positive,
            names_to = “names”,
            values_to_ “value”)

# using ggplot
df_tidy %>% ggplot(aes(x = date, y = value)) +
    geom_line() +
    facet_grid(names ~ area)

I recommend the Wickham's book ggplot2: elegant graphics for data analysis . It has a plenty of examples to explore!