Wish: a way to define "presets" for chunk options for use in long documents / books

[gavinsimpson]

Description

When writing longer documents (i.e. presentations for lectures, papers, books, …) I often find myself writing the same few sets of chunk options over and over again. For example:

• a chunk to load packages at the start of a chapter or slide deck, which I use echo: false and output: false and message: false etc
• chunk options with fig-width and fig-height defined for document figures containing a single full-width plot or for a row of two plots, etc

While one can set a single set of chunk defaults per output format, flexibility beyond that is (as far as I can tell) not possible. I would like to propose that it be possible that classes of chunks be defined in the YAML header or _quarto.yml, and subsequently applied to individual chunks via the chunk option class. I.e. something like

chunks:
  setup:
    echo: false
    include: false
  one-fig-full:
    echo: false
    fig-width: 7
    fig-asp: 1/1.77777
    dpi: 150
    out.width: 100%
    fig.align: center
  one-fig: 
    echo: false
    fig-width: 7
    fig-asp: 1/1.77777
    dpi: 150
    out.width: 80%
    fig.align: right
  four-fig:
    echo: false
    fig-width: 7
    fig.asp: 1
    dpi: 150:
    fig-align: center

then

```{r}
#| label: doc-setup
#| class: setup
library("ggplot2")
library("mgcv")
```

or

```{r}
#| label: fig-plot1
#| class: one-fig-full
df |>
  ggplot(
    aes(
      x = x
      y = y
    )
  ) +
  geom_point()
```

It would be nice to be able to inherit options, for example:

chunks:
  setup:
    echo: false
    include: false
  figs: 
    echo: false
    fig-width: 7
    fig-asp: 1/1.77777
    dpi: 150
    out.width: 100%
    fig.align: center
  one-fig-full-show:
    inherit: figs
    echo: true

[cderv]

There is indeed no cross engine way in Quarto yet to do that. Only thing close to this are

• The execute configuration, for any option that compatible across engines: https://quarto.org/docs/computations/execution-options.html
• Some specific support for engine options https://quarto.org/docs/computations/execution-options.html#knitr-options like setting opts_knit and opts_chunk using YAML configuration for all the chunk in the doc.

If you are working with R documents using knitr engine, then you could leverage the knitr's feature.

I am thinking of knitr::opts_template()

• https://bookdown.org/yihui/rmarkdown-cookbook/opts-template.html

This is a way to define options set, and named them. Then they can be used using opts.label.

---
title: "TEST"
format: html
---

```{r}
#| label: setup
#| include: false
knitr::opts_template$set(
  fullwidth = list(
    fig.width = 10, fig.height = 6, fig.retina = 2, out.width = '100%'
  )
)
```

```{r}
#| opts-label: fullwidth
plot(cars)
```

We could add opts_template support for knitr specific options maybe 🤔

What you describe is more generic and is a way to do generalize the knitr opts_template feature. Could be interesting but limited to common cell option across engine. 🤔