Improving plot sizing for multi row / multi column plot for qmd --> pdf

[tomasrei]

The goal of this REPREX is to find a method that applies less guesswork when adding new plot-grids to a pdf-report by using sensible defaults.

Since I have had some issues with plot scaling when rendering pdf-reports using quarto, I came up with a solution that I think works ok.

I worked on this after submitting Issue #14252.

The idea is the put the code in #| label: hidden-function in a separate file -- for decluttering purposes -- and use source(file) in the .qmd file that generates your plots.

Also, I tried using the quarto default #| layout-ncol: 2, but that produced way too much whitespace between the two plots, so I use patchwork here instead. I'm sure a native quarto solution can be found.

Appriciate any feedback / suggestions!

---
title: "Reprex: Quarto layout-ncol vs patchwork"
format:
  pdf:
    fig-pos: 'H'
geometry:
  - top=3cm
  - bottom=3cm
  - left=3cm
  - right=3cm
knitr:
  opts_chunk:
    echo: false
    warning: false
    message: false
    include: false
---

#| label: setup
library(tidyverse)
library(patchwork)
library(S7)

theme_set(theme_bw(base_size = 13))

#| label: hidden-function

FigureSettings <- new_class(
  "FigureSettings",
  properties = list(
    fig_width         = new_property(class_double, default = 6),
    fig_asp           = new_property(class_double, default = 0.618),
    out_frac          = new_property(class_double, default = 0.70),
    additive_constant = new_property(class_double, default = 0.5),

    out_width = new_property(
      class_character,
      getter = function(self) paste0(round(self@out_frac * 100), "%")
    )
  ),
  validator = function(self) {
    if (self@fig_width <= 0)                      return("fig_width must be positive")
    if (self@fig_asp   <= 0)                      return("fig_asp must be positive")
    if (self@out_frac  <= 0 || self@out_frac > 1) return("out_frac must be in (0, 1]")
  }
)

apply_fig_settings <- new_generic("apply_fig_settings", "settings")

method(apply_fig_settings, FigureSettings) <- function(settings) {
  fw <- settings@fig_width
  fa <- settings@fig_asp
  of <- settings@out_frac
  ac <- settings@additive_constant

  knitr::opts_chunk$set(
    fig.width = fw,
    fig.asp   = fa,
    fig.align = "center",
    out.width = settings@out_width
  )

  knitr::opts_hooks$set(plot_layout = function(options) {
    parts <- as.integer(strsplit(options$plot_layout, "x")[[1]])
    nrow  <- parts[1]
    ncol  <- parts[2]

    if (ncol > 1) {
      fig_w <- fw / of
      fig_h <- nrow * (fig_w / ncol) * fa + ac
      options$fig.width  <- fig_w
      options$fig.height <- fig_h
      options$out.width  <- "100%"
    } else {
      options$fig.height <- fw * fa * nrow + ac
    }
    options$fig.asp <- NULL
    options
  })

  invisible(settings)
}

#| label: visible-settings

fs <- FigureSettings(
  fig_width         = 6,
  fig_asp           = 0.618,
  out_frac          = 0.70,
  additive_constant = 0.2
)
apply_fig_settings(fs)

#| label: generate-plots
p1 <- ggplot(mtcars, aes(x = disp, y = mpg)) +
  geom_point() +
  labs(x = "Displacement (cu. in.)", y = "Miles per gallon")

p2 <- ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  labs(x = "Weight (1000 lbs)", y = "Miles per gallon")

Single plot (default sizing)

#| include: true
#| label: fig-single

p1

Two plots side by side (plot_layout: "1x2")

#| include: true
#| label: fig-layout-ncol
#| fig-cap: "Two plots side by side using patchwork"
#| plot_layout: "1x2"

wrap_plots(p1, p2, ncol = 2) +
  plot_layout(guides = "collect")

Reference: R4DS — Figure sizing

plot_layout: "1x2" triggers the knitr hook registered by apply_fig_settings,
which widens fig.width to fill full text width while preserving the text-scale
invariant (out.width / fig.width = constant). Each subplot renders with
fig.asp aspect ratio but is shorter than the single plot, because it is also
narrower. Of course, plot_layout: 1x2 can be replaced by whatever size grid is desired.