ggplot: grouping and plotting multiple lines, but handle them separately

Question

I have this dataframe: df_long:

year       variable      value    
1970       Argentina     20
1980       Argentina     30
1990       Argentina     80
1970       Belgium       10
1980       Belgium       22
1990       Belgium       80
1970       U.S.          12
1980       U.S.          36
1990       U.S.          80
1970       Australia     11
1980       Australia     12
1990       Australia     90

I did this:

  p <- ggplot(df_long, aes(year, value)) +
geom_line(aes(colour = variable, group = variable))
show(p)

And I can see 4 lines on the same plot, one for each country. But I don't know how to select these lines separately to manipulate them. For example, to give a red colour to the Argentina line, etc. Also, I would like to add a facet_grid() with 2 columns so I can see on the left plot lines from Argentina + Australia and on the right plot the lines from Belgium + U.S.

How can I divide the groupings so that I can do this?

Answer 1

Try this:

1. Add new column to your tibble:

   df <- df %>% mutate(group = case_when(
     variable %in% c("Australia", "Argentina") ~ "group 1",
     variable %in% c("Belgium", "U.S.") ~ "group 2"
   ))
   

2. Plot new df:

   ggplot(df, aes(year, value)) +
     geom_line(aes(colour = variable, group = variable)) + 
     scale_color_manual(values=c("red", "blue", "green", "orange")) + 
     facet_wrap(~group)
   

With scale_color_manual() you can control the colors individually for each line