Shared legend in subplots

Question

I'm trying to translate some of my R code to Julia. I mainly struggle with the difference in plotting as I'm very used to ggplot2.

There I can do:

mpg %>% 
ggplot(aes(x = displ, y = cyl, color = manufacturer)) + 
geom_point() + 
facet_wrap(~class)

With this I get subplots, consistent x- and y-axes, a shared legend, and much more. How would I achieve this with Julia, say the GR backend?

Update: The mpg data set looks like:

# A tibble: 234 × 11
   manufacturer model      displ  year   cyl trans      drv     cty   hwy fl    class  
   <chr>        <chr>      <dbl> <int> <int> <chr>      <chr> <int> <int> <chr> <chr>  
 1 audi         a4           1.8  1999     4 auto(l5)   f        18    29 p     compact
 2 audi         a4           1.8  1999     4 manual(m5) f        21    29 p     compact
 3 audi         a4           2    2008     4 manual(m6) f        20    31 p     compact
 4 audi         a4           2    2008     4 auto(av)   f        21    30 p     compact
 5 audi         a4           2.8  1999     6 auto(l5)   f        16    26 p     compact
 6 audi         a4           2.8  1999     6 manual(m5) f        18    26 p     compact
 7 audi         a4           3.1  2008     6 auto(av)   f        18    27 p     compact
 8 audi         a4 quattro   1.8  1999     4 manual(m5) 4        18    26 p     compact
 9 audi         a4 quattro   1.8  1999     4 auto(l5)   4        16    25 p     compact
10 audi         a4 quattro   2    2008     4 manual(m6) 4        20    28 p     compact
# … with 224 more rows

and the output I'm after would look something like:

Answer 1

The easiest way to do this at present might be with Makie.jl, which gives you very granular control over the plotting process. For example:

# using GLMakie # If you want an interactive plot window and raster graphics
# or
using CairoMakie # If you want to save vector graphics

fig = Figure()
ax1 = Axis(fig[1, 1])
ax2 = Axis(fig[1, 2])
ax3 = Axis(fig[2, 1:2])
l1 = lines!(ax1, 0..10, sin, color=:red)
l2 = lines!(ax2, 0..10, cos, color=:blue)
l3 = lines!(ax3, 0..10, sqrt, color=:green)
ax1.ylabel = "amplitude"
ax3.ylabel = "amplitude"
ax3.xlabel = "time"
Legend(fig[1:2, 3], [l1, l2, l3], ["sin", "cos", "sqrt"])
fig

and optionally

save("filename.ext", fig)

yields

There are a number of good examples and tutorials in https://makie.juliaplots.org/v0.15.1/tutorials/basic-tutorial/ and https://lazarusa.github.io/BeautifulMakie/

If you tend to like the "grammar of graphics" style, you might also check out AlgebraOfGraphics.jl, which is built on top of Makie, or (though I haven't tried it in some time) Gadfly.jl, which was actually one of the first plotting packages in Julia.