Some Quarto Tips for Academic Presentation

Are You a Beamer Fan?

The other day, I used slides made with Quarto in a presentation at a conference. In the Economics community, 98% of people use Beamer of \(\LaTeX\), and about 2% use PowerPoint for their presentations. I personally don’t like Beamer’s design, and I think PowerPoint has a problem with maintainability (i.e., can it be easily changed) in case of ongoing projects. I like Quarto for the following reasons:

1. Reasonably good design. And highly customizable.
2. Time saving. Slides are written in the markdown notation, so you can make it with the same amount of effort as Beamer (unless you care about the design😉)
3. Easily maintainable. Variables can be used in the text, so the numbers are automatically updated even if the model or analysis is slightly changed.

Here, I write some tips on Quarto for academic presentations. For the basic slide creation in Quarto, please refer to the official documentation or Tom Mock’s slides at the RStudio conference. The slides used at the conference presentation are not yet ready for public release, so I prepare these example slides

Slides   PDF   Code

Data

I render tables and plots inside of slides. In other words, I am not using the image files for the article. This is because

1. Proper font sizes in the article are too small in presentation slides
2. Highlighting is not easy. You need to create another figure/table or use complicated TikZ
3. I want to unify the design of slides and figures&tables

Hence, I create and save a data frame in a separate file and load it just before plotting it.

load("tb_hoge.rds")
tb_hoge |>
  ggplot(aes(x, y)) +
  geom_point()

You can use this data frame to refer to its values in a slide text.

In 2021, `r tb_hoge$value[tb_hoge$year == 2021]`% of people…

This is convenient in case you change your analysis slightly and the values in tb_hoge.rds change.¹ The values will be updated by re-rendering slides.

Theme

There are 11 built-in themes provided for Reveal presentations. These are good designs, but to match them with figures&tables, I write custom.scss and make my own theme. Currently, it is like xaringanthemer’s style_mono_accent() theme. You can check about the customizable parts in the official document.

/*-- scss:defaults --*/

@import url(https://fonts.googleapis.com/css?family=Montserrat:300,300i&display=swap);
@import url(https://fonts.googleapis.com/css?family=Josefin+Sans&display=swap);
@import url(https://fonts.googleapis.com/css?family=Fira+Mono&display=swap);

// fonts
$font-family-sans-serif: Montserrat, sans-serif !default;
$font-family-monospace: "Fira Mono", monospace  !default;

// colors
$body-bg: #fff !default;
$body-color: #272822 !default;
$link-color: #055099 !default;

// headings
$presentation-heading-font: "Josefin Sans", sans-serif !default;
$presentation-heading-color: #1C5253 !default;

$h1-font-size: 1.6em !default;
$h2-font-size: 1.3em !default;
$h3-font-size: 1.15em !default;
$h4-font-size: 1em !default;

// code blocks
$code-block-border-color: #93a1a1 !default;
$code-color: $presentation-heading-color;

//
// Color system
//

// stylelint-disable
$white:    #fff !default;
$gray-100: #fdf6e3 !default;
$gray-200: #eee8d5 !default;
$gray-300: #dee2e6 !default;
$gray-400: #ced4da !default;
$gray-500: #adb5bd !default;
$gray-600: #839496 !default;
$gray-700: #495057 !default;
$gray-800: #073642 !default;
$gray-900: #002b36 !default;
$black:    #000 !default;

/*-- scss:rules --*/

.title{
    color: $white;
    font-size: 2.5em;
    font-family: $presentation-heading-font;
    position: absolute;
    top: 20%
}

.subtitle{
    color: $gray-100;
    font-size: $h2-font-size;
    font-family: $presentation-heading-font;
    position: absolute;
    top: 33%
}


.author {
    color: $white;
    font-size: $h3-font-size;
    font-family: $presentation-heading-font;
    position: absolute;
    bottom: 10%;
}

.date {
    color: $white;
    font-size: $h4-font-size;
    font-family: $presentation-heading-font;
    position: absolute;
    bottom: 5%;
}


.message{
    color: $presentation-heading-color;
    font-size: $h2-font-size;
    font-family: $presentation-heading-font;
    text-align: center;
}

.space-left {
    margin-left: 5%;
}


.center-xy {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    -ms-transform: translateY(-50%), translateX(-50%);
    transform: translateY(-50%), translateX(-50%);
}


.small {
    font-size: 0.8em
}

.Large {
    font-size: 1.6em
}

section.has-dark-background a {
    color: $white;
    border-style: dashed;
    border-bottom-width: 1px;
}

section.has-dark-background a:hover {
    color: $white;
    border-bottom: solid
}

Ad-hoc CSS

I write frequently used CSS settings in custom.css, but sometimes I want to use a CSS environment on an ad-hoc basis (for example, to change the font size slightly.)

In these cases, you can write them in style= environment:

::: {style="font-size: 0.68"}

Sentences you want to make smaller

:::

Fragments

Quarto (or Reveal.js) allows some complicated animation. If you are interested, you might want to see Tom Mock’s this part of the slides.

Apart from this, as discussed here, the original fragment separator . . . does not correctly work in environments like columns. From my experience, fragment environment solves them.

Plots

Theme

Minimizing elements is a starting point of slide design. For that purpose, it is important to use the same fonts and colors for figures (and tables) as the slides. This is the reason why I used to use xaringanthemer, which automatically generates the ggplot2 theme corresponding to the slides’ theme. Unfortunately, there have been no packages for Quarto slides (as far as I know), I declare this theme_quarto() function.

blend_colors <- function(x, y, alpha = 0.5) {
  x <- colorspace::hex2RGB(x)
  y <- colorspace::hex2RGB(y)
  z <- colorspace::mixcolor(alpha, x, y)
  colorspace::hex(z)
}
color_blender <- function(x, y) function(alpha = 0.5) blend_colors(x, y, alpha)
theme_quarto <- function (
    text_color = color_text,
    background_color = color_bg,
    text_font = font_text,
    text_font_size = 30,
    accent_color = color_base,
    title_font = font_title,
    title_font_size = 30
){
    blend <- color_blender(text_color, background_color)
    ggplot2::theme(
        line = ggplot2::element_line(color = blend(0.2)),
        rect = ggplot2::element_rect(fill = background_color),
        title = ggplot2::element_text(
            color = accent_color,
            family = title_font,
            size = title_font_size
        ),
        plot.background = ggplot2::element_rect(
            fill = background_color,
            color = background_color
        ),
        panel.background = ggplot2::element_rect(
            fill = background_color,
            color = background_color
        ),
        panel.grid.major = ggplot2::element_line(
            color = blend(0.8),
            inherit.blank = TRUE
        ),
        panel.grid.minor = ggplot2::element_line(
            color = blend(0.9),
            inherit.blank = TRUE
        ),
        axis.title = ggplot2::element_text(size = title_font_size * 0.8),
        axis.ticks = ggplot2::element_line(color = blend(0.8)),
        axis.text = ggplot2::element_text(color = blend(0.4), size = title_font_size * 0.7),
        legend.key = ggplot2::element_rect(fill = "transparent", colour = NA),
        legend.text = ggplot2::element_text(size = title_font_size * 0.8, family = title_font),
        plot.caption = ggplot2::element_text(
            size = text_font_size * 0.8,
            color = blend(0.3)
        )
    )
}

While the original xaringanthemer::theme_xaringan() redefines the primary color of ggplot2::geom_* by ggplot2::update_geom_defaults, my function does not. I did not overwrite it because color palettes must be specified manually for 2+ color cases, anyway. You can use it like:

color_base <- "#1C5253"
tb_hoge |>
  ggplot(aes(x, y)) +
  geom_point(color = color_base) +
  theme_quarto()

Highlighting

The most famous way to highlight plots should be gghighlight. You can proceed with your stories smoothly and clearly by

First Slide

p <- tb_hoge |>
  ggplot(aes(x, y)) +
  geom_col(color = color_base) +
  theme_quarto()

p

Second Slide

p + gghighlight(x == "Japan")

Tables

markdown vs. kableExtra vs. gt?

I think they are three popular ways to create tables in HTML slides. while each of them has pros and cons, I am using gt because

Markdown Table

• No highlighting
• No multirow nor multicol from \(\LaTeX\)

kableExtra

• Syntax is a little more complicated than gt (e.g., need to mutate a string column for percentages.)
• Highlighting is slightly more complicated than gt

Note that I use kableExtra for tables in an article due to the following problem.

Problems with Mathematic Expressions

Unfortunately, it is difficult to use mathematical expressions in a table in Quarto. gt does not support \(\LaTeX\) notation.² Also, mathematical expressions of kableExtra are not rendered in Quarto (GitHub Issue). You can solve it by

kableExtra::kbl(data, format="markdown")

but it contains the abovementioned disadvantages of markdown tables.

Then, I compromise by using

• Unicode Greek letters (θ, τ, δ, etc.)
• HTML tags (<sup> and <sub>)

and evaluating them by gt::fmt_markdown(). Mathematical expressions in tables are usually simple, so I don’t have any problems so far.

tibble(a = c("θ = 0", "τ<sup>δ-1</sup>")) |>
  gt() |>
  fmt_markdown(columns = everything())

Highlighting

The gt package itself can also highlight cells in a table with the function tab_style(). However, this requires redundant writing, so gtExtras::gt_highlight_rows() and gtExtras::gt_highlight_cols() are useful if you want to highlight row/column-wise.

Export

HTML or PDF?

Although I think you use a prepared PC for your presentation, since it is difficult to imagine a PC without a browser, the HTML format is also acceptable. If you write the following in the YAML header, only one self-contained HTML file will be output. So you can easily carry it around like a PDF file.³

format:
  revealjs:
    standalone: true
    embed-resources: true

However, you will be asked to submit your slides in PDF format in various situations. And whether or not you actually present your presentation in PDF format, it is a good idea to have PDF slides on hand for insurance purposes.

1. Open the HTML file in your browser and press E
2. Click “Print” on the browser, then “Save as PDF”

If you want to separate fragments, specify pdf-separate-fragments: true in YAML.

Problems with Hyperlink

A hyperlink that jumps to each slide is essentially a reference to an <h2> tag, so the link can be written as:

## A Slide {#sec-slide}

<a href="#/sec-detail">detail↗</a>

## A Detail Slide {#sec-detail}

<a href="#/sec-slide">↩︎</a>

However, as far as I know, the link is not reflected in the above PDF output. If anyone knows a solution to this problem, I would appreciate it if you could let me know.

Fin.

These are some of my ideas for using Quarto for academic presentations. I think that Quarto’s slides are quite suitable for academic presentations, because of their simple syntax, high degree of freedom in design, and high maintainability in numbers. I hope this is useful for you.

Footnotes

1. In economics, changing the age group of the sample or the parameters of the model sometimes lead to changes in the results. In addition, we sometimes found mistakes in cleaning the data.

2. This issue has been raised in 2019, but it does not seem to be solved quickly.

3. The option self-contained: true produces a deprecated warning.