< xfun::numbers_to_words(12) n_participants
Literate programming
Literate programming is the practice of mixing text and executable code in the same document, making it possible to write reproducible documents. There are four engines for executing code in Quarto documents:
 knitr (supports R, Python, Julia, and more)
 jupyter (Python only)
 IJulia (Julia only)
 Observable JS (Observable JS only)
All engines support executing code in code blocks within a document, which can be used to execute code and include its output in a document. Code blocks can produce a wide variety of outputs, including plots, tabular output from data frames, and plain text. The behaviour of code execution and output can be set with Quarto’s Execution Options.
knitr, jupyter, and Observable JS also support executing inline code within markdown text, which can be used to allow narrative to automatically use the most up to date computations. The syntax for inline code varies across the engines.
The remainder of this post covers some useful literate programming practices when writing reproducible documents with the knitr engine.
Plain text outputs
Most code you write will be output as plain text. Depending on the purpose of a document, it might be fine to leave that output as is, or you might want to format the text, include it inline, and so forth.
For example, say you wanted to report the number of participants in a study you ran. Rather than writing a sentence like this:
There were twelve participants in the study.
You could get the number of participants computationally, format that number into the word “twelve”, and include it in the sentence using inline code:
There were
`r n_participants`
participants in the study.
This sentence would become “There were twelve participants in the study.” when you render the document. Likewise, if the number of participants changed, the number reported in the sentence would change the next time the document rendered (as long as the R object storing the number of participants knew about the change).
If there are many values you need to report inline, storing them in a list is a good practice. For an overview of this approach, see:
 Lists are my secret weapon for reporting stats with knitr by Tristan Mahr
Figure and table outputs
Figures and tables produced by code blocks have unique parameters you can use to adjust their layout, add captions, or make them crossreferenceable. See the Quarto documentation for details:
Equations
Quarto features extensive support for writing beautiful math equations with LaTeX math expressions authored using standard Pandoc markdown syntax: Use $
delimiters for inline math and $$
delimiters for display math. Provide an #eq
label immediately after a display math equation to make it referenceable.
Markdown Syntax  Output 

inline math: $E = mc^{2}$ 
inline math: E=mc^{2} 
display math:

display math: E = mc^{2} 
display math with label:

display math with label: E = mc^{2} \tag{1} 
Math expressions can be rendered in any of Quarto’s output formats, but different rendering methods are used depending on the format:
html
offers several math rendering methodspdf
uses LaTeX (including raw LaTeX)docx
uses Microsoft Word’s equation environment
To learn more about writing LaTeX math expressions, see:
Using inline R code in math equations
Inline R code `r `
can be used within inline or display math to include code output in math equations.
< lm(mpg ~ am, data = mtcars)
mtcars_fit < coef(mtcars_fit)["(Intercept)"]
coef_int < coef(mtcars_fit)["am"] coef_am
Inline math: $\mathrm{\widehat{mpg}} = `r coef_int` + `r coef_am`(\mathrm{am})$
Inline math: \mathrm{\widehat{mpg}} = 17.1473684 + 7.2449393(\mathrm{am})
The same approach also works for display math.
Using math equations in plots
Both base R and ggplot2 plots feature support for writing beautiful math equations with plotmath expressions. Equations can be used in plot labels, legends, and text.
If you would rather write equations using LaTeX math expressions, the latex2exp package can be used to parse and convert LaTeX to plotmath expressions.^{2} Learn more on the package website.
ggplot2 also includes some convenience functions for using plotmath in plot labels:
label_parsed()
interprets labels as plotmath expressionslabel_bquote()
offers a flexible way of labelling facet rows or columns with plotmath expressions
Footnotes
MathJax is an opensource JavaScript rendering engine for LaTeX math expressions. It is the default rendering method in Quarto HTML documents.↩︎
There is also an open issue to support LaTeX math expressions using markdown in the ggtext package.↩︎