plot_layout `axis_titles = "collect"` has unusual behaviour for non-square assemblies

[jack-davison]

See examples below - when you have a perfect 3x3 grid you get a single ylab on the LHS, but when you have a missing panel you end up with two - one ylab centred on the top 2x3 area and then another for the bottom row, which does look a bit odd!

Is this expected behaviour for this option?

Cheers!

library(patchwork)

# I know this is deprecated, but it's the quickest way to get a ggplot2...
theplot <- ggplot2::qplot(iris$Sepal.Length) + ggplot2::labs(y = "Axis")
#> Warning: `qplot()` was deprecated in ggplot2 3.4.0.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.

# this is okay
wrap_plots(rep(list(theplot), 9), nrow = 3) +
  plot_layout(axes = "collect")

# this looks a bit weird
wrap_plots(rep(list(theplot), 8), nrow = 3) +
  plot_layout(axes = "collect", axis_titles = "collect")

^{Created on 2024-08-08 with reprex v2.1.1}

[jack-davison]

On reflection, I can guess why this is happening - the x-axis is "split" so you have that gap for the smaller x-axis to be drawn, which I guess is causing the y-labs to be drawn separately.