Introduction

Make sure to use the right aspect ratio

To use all available screen real estate.

\[ \text{Aspect ratio} = \frac{\text{width}}{\text{height}} \]

• Default: \(\frac{1050}{700} = 1.5\)

• My laptop: \(\frac{1050}{682.26} = 1.539\)

Define a custom aspect ratio in the YAML:

yaml

format: 
  revealjs:
    height: 682.26

Absolute positioning

![](img/seaotters.jpg){.absolute top="-10%" right="-40%" height="100%"}

Do note that the text will not respect the image with absolute positioning so that you might get overlaps.

Columns helps you maximise your screen real estate

# What day of the week is it?
lubridate::wday("2026-07-09", label = TRUE)

[1] Thu
Levels: Sun < Mon < Tue < Wed < Thu < Fri < Sat

:::: {.columns}

::: {.column width="48%"}

Example of use. This is column 1. Tweak the widths to accomodate images or code chunks.

![](img/badger.jpg){width=70%}

# What day of the week is it?
lubridate::wday("2026-07-09", label = TRUE)

:::

::: {.column width="52%"}

And this is column 2. 

:::

::::

Display and run code: My two approaches

1. For simple, one line pieces of code or a small pipeline: Open up a script and do some live coding. Prepare a script beforehand to look at. Allows students to copy off the screen.
2. For longer pieces of code: Use fragments to show the code, and then the output, staggered.

Using fragments

Fragments reveal parts of the slide gradually. Can be stylised extensively.

#| output-location: fragment

library(tidyverse)

penguins |> 
  filter(species == "Gentoo") |> 
  group_by(sex) |> 
  summarise(
    body_mass_m = mean(body_mass, 
                       na.rm = TRUE),
    body_mass_sd = sd(body_mass, 
                      na.rm = TRUE))

library(tidyverse)

penguins |> 
  filter(species == "Gentoo") |> 
  group_by(sex) |> 
  summarise(
    body_mass_m = mean(body_mass, 
                       na.rm = TRUE),
    body_mass_sd = sd(body_mass, 
                      na.rm = TRUE))

# A tibble: 3 × 3
  sex    body_mass_m body_mass_sd
  <fct>        <dbl>        <dbl>
1 female       4680.         282.
2 male         5485.         313.
3 <NA>         4588.         338.

Exercise sheet with answers

To avoid tedious copy-pasting of answer sheets for exercises, use parameters.

Define a YAML parameter hide_answers that is true/false. Wrap the content in a hide content div (:::) with R code (if) conditional on the parameter.

How this looks in practice:

yaml

params: 
  hide_answers: true

In your presentation slide:

slide

`r if (params$hide_answers) "::: {.content-hidden}"`

[Some code]

`r if (params$hide_answers) ":::"`

With hide_answers = true

Exercise 1

The Palmer penguins dataset has measured penguins’ properties in mm. Turn the measurements into cm.

With hide_answers = false

Exercise 1

The Palmer penguins dataset has measured penguins’ properties in mm. Turn the measurements into cm.

library(tidyverse)

penguins |> 
  mutate(
    across(c(bill_len, bill_dep, flipper_len),
           \(x) x / 10 )
  ) |> 
  head()

  species    island bill_len bill_dep flipper_len body_mass    sex year
1  Adelie Torgersen     3.91     1.87        18.1      3750   male 2007
2  Adelie Torgersen     3.95     1.74        18.6      3800 female 2007
3  Adelie Torgersen     4.03     1.80        19.5      3250 female 2007
4  Adelie Torgersen       NA       NA          NA        NA   <NA> 2007
5  Adelie Torgersen     3.67     1.93        19.3      3450 female 2007
6  Adelie Torgersen     3.93     2.06        19.0      3650   male 2007