{ggplot2} plot-height determined by facet row count: halve the height of the output if the second facet row is missing

responsive-facet-height.R

# Calculate how many plots will be produced
count_plots <- function(df, var) {
  length(unique(df[[var]]))
}

# Plot faceted chart, save with height dependent on plot count
write_responsive_facets <- function(
  df, 
  var = "species",
  plot_count = count_plots(df, var), 
  facet_cols = 2,
  write_dir
) {

  p <- df |> 
    ggplot2::ggplot(ggplot2::aes(bill_length_mm, bill_depth_mm) ) +
    ggplot2::geom_point() + 
    ggplot2::facet_wrap(~species, ncol = facet_cols)
  
  # Save at half-height if only one facet row is used
  if (plot_count > facet_cols) responsive_height <- 10
  if (plot_count <= facet_cols) responsive_height <- 5

  ggplot2::ggsave(
    glue::glue("{write_dir}/test-{plot_count}-plots.png"),
    width = 10,
    height = responsive_height
  )

}

# Data with three plots: 2 on top facet row, 1 below
peng_3_sp <- palmerpenguins::penguins |>
  tidyr::drop_na(species, bill_length_mm, bill_depth_mm)

# Data with two plots: 2 on top facet row, zero below
peng_2_sp <- peng_3_sp |> dplyr::filter(species != "Gentoo")

write_responsive_facets(peng_3_sp)  # 2x2 facets, height 10
write_responsive_facets(peng_2_sp)  # 1x2 facets, height 5

With three plots:

With two plots: