Setup
Loading epoxy adds four new knitr
engines, or chunk types. Each type lets you intermix text with R
code or data (expr in the table below), and each is geared
toward a different output context.
| Engine | Output Context | Delimiter |
|---|---|---|
epoxy |
all-purpose markdown | {expr} |
epoxy_html |
HTML | {{expr}} |
epoxy_latex |
LaTeX | <<expr>> |
whisker |
all-purpose | mustache template language |
⚠️ Caution: Previously, epoxy provided a
glue engine, but this conflicts with a similar chunk engine
by the glue package. You can
update existing documents to use the epoxy engine, or you
can explicitly use epoxy’s glue chunk by including the
following in your setup chunk.
Using epoxy chunks
To use epoxy in your R Markdown document, create a new chunk using the engine of your choice. In that chunk, write in markdown, HTML, or LaTeX as needed, wrapping R expressions inside the delimiters for the epoxy chunk.
```{epoxy}
The average speed of the cars was **{mean(cars$speed)} mph.**
But on average the distance traveled was only _{mean(cars$dist)}_.
```The average speed of the cars was 15.4 mph. But on average the distance traveled was only 42.98 ft.
epoxy is built around glue::glue(), which
evaluates the R expressions in the { } and inserts the
results into the string. The chunk above is equivalent to this call to
glue::glue():
glue::glue("The average speed of the cars was **{mean(cars$speed)} mph**.
But on average the distance traveled was only _{mean(cars$dist)} ft_.")
#> The average speed of the cars was **15.4 mph**.
#> But on average the distance traveled was only _42.98 ft_.One immediate advantage of using epoxy instead of
glue::glue() is that RStudio’s autocompletion feature works
inside epoxy chunks! Typing cars$ in the chunk
will suggest the columns of cars.
Inline transformers
epoxy provides inline transformations inspired by cli’s inline
markup. This transformer is enabled by default in
epoxy(), epoxy_html() and
epoxy_latex() and their respective knitr chunk engines.
Here’s an example using a small list containing data about a
movie (expand the section below to see the full code for
movie). We can use the inline transformer to format the
replacement text as we build up a description from this data.
Movie data
```{epoxy}
The movie {.emph {.titlecase movie$title}}
was released in {.strong movie$year}.
It earned {.dollar movie$domgross}
with a budget of {.dollar movie$budget},
and it features movie stars
{.and movie$actors}.
```The movie Back to the Future Part II was released in 1989. It earned $118,450,002 with a budget of $40,000,000, and it features movie stars Michael J. Fox, Christopher Lloyd, Lea Thompson, and Thomas F. Wilson.
Read more about inline transformations in
?epoxy_transform_inline.
Transform replaced values
You can use the epoxy_transform_wrap() with the
epoxy_transform chunk option to wrap the evaluated R
expression in formatting or templating text. Or you can use the pre-set
epoxy_transform_bold(),
epoxy_transform_italic(), or
epoxy_transform_code() transformers or with
epoxy_transform().
```{epoxy, .transformer = epoxy_transform("bold")}
All cars stopped between {min(cars$dist)} and {max(cars$dist)} feet
from a starting speed of {min(cars$speed)}---{max(cars$speed)}
```All cars stopped between 2 and 120 feet from a starting speed of 4—120 mph.
epoxy chunks are vectorized
Unlike inline R code, the epoxy chunks are vectorized.
This can be something to watch out for or it can be an advantage:
```{epoxy}
{1:4}. "{letters[1:4]}" is for {c("apple", "banana", "coconut", "donut")}
```- “a” is for apple
- “b” is for banana
- “c” is for coconut
- “d” is for donut
You can collapse fields automatically using the
epoxy_transform_collapse() transformer. You can then choose
how vectors are collapsed by adding *, &
or | to the end of the expression.
-
*collapses with commas, e.g.{letters[1:3]*}. -
&collapses with commas and adds" and "between the last two items -
|collapses with commas and adds" or "between the last two items.
```{epoxy, .transformer = epoxy_transform("collapse")}
- The first three letters are {letters[1:3]*}.
- When capitalized, they are {LETTERS[1:3]&}.
- They're indexed by {1:3|}.
```- The first three letters are a, b, c.
- When capitalized, they are A, B, and C.
- They’re indexed by 1, 2, or 3.
You can change the separator between entries and between the last
entry using the sep, last and the
_and and _or specific arguments of the
epoxy_transform_collapse() function.
Templating with epoxy chunks
It’s also possible to create a reusable template. Use the
ref.label chunk option to reuse a template using the values
in the .data chunk option, which can be a list or data
frame.
mpg <- data.frame(
manufacturer = c("Chevrolet", "Dodge", "Ford"),
model = c("Malibu", "Caravan", "Expedition"),
cty = c(19, 7, 11),
hwy = c(27, 24, 17)
)```{epoxy car-name, eval=FALSE}
- A {manufacturer} {model} gets {cty} city and {hwy} highway miles per gallon.
```
```{epoxy ref.label="car-name", .data = mpg}
```- A Chevrolet Malibu gets 19 city and 27 highway miles per gallon.
- A Dodge Caravan gets 7 city and 24 highway miles per gallon.
- A Ford Expedition gets 11 city and 17 highway miles per gallon.
Whisker engine
Sometimes the epoxy engine doesn’t quite deliver the
template power you need. In these cases, you can use the
whisker engine instead.
```{r}
contestant <- list(name = "R User", value = 1000, taxed = 600, in_ca = TRUE)
```
```{whisker .data = contestant, echo=FALSE}
Hello {{name}}:
You have just won ${{value}}!
{{#in_ca}}
Well, ${{taxed}}, after taxes.
{{/in_ca}}
```
contestant <- list(name = "R User", value = 1000, taxed = 600, in_ca = TRUE)Hello R User: You have just won $1000! Well, $600, after taxes.
HTML and LaTeX chunks
Markdown chunks
The epoxy chunk engine can be used in any output format.
In practice, it works best in markdown (i.e. generally in R Markdown or
Quarto)
where it renders as:
- **Chevrolet** _Malibu_
- **Dodge** _Caravan_
- **Ford** _Expedition_If you’re writing for an HTML or LaTeX output, however, you may need
to write literal HTML or LaTeX in your document. With the
epoxy chun, you’d need to escape any { or
} in your text by doubling them, otherwise the content
within will be treated as a template expression. To avoid this friction,
epoxy provides two additional chunk engines, epoxy_html for
writing raw HTML and epoxy_latex for writing raw LaTeX.
Raw HTML chunks
Use the epoxy_html block to epoxy (glue) R and HTML
together. The output is raw HTML. By
default, expressions in these types of blocks are wrapped in
{{ and }}, like whisker templates above.
<ul>
```{epoxy_html, .data = mpg}
<li><strong>{{manufacturer}}</strong> <em>{{model}}</em></li>
```
</ul><ul>
```{=html}
<li><strong>Chevrolet</strong> <em>Malibu</em></li>
<li><strong>Dodge</strong> <em>Caravan</em></li>
<li><strong>Ford</strong> <em>Expedition</em></li>
```
</ul>Notice that the output is HTML but wrapped in a pandoc raw html block, which tells pandoc that the content is HTML that shouldn’t be modified1. It also means that the output of the chunk will only be included in HTML documents.
If your epoxy_html block is contained within another a
raw html block, or if you want to force the output to appear, you can
set the chunk option html_raw = FALSE.
````{=html}
<ul>
```{epoxy_html, .data = mpg, html_raw = FALSE}
<li><strong>{{manufacturer}}</strong> <em>{{model}}</em></li>
```
</ul>
````epoxy_html uses two custom transformers,
epoxy_transform_inline() and
epoxy_transform_html(), applying the html transformer
before the inline transformer. With epoxy_transform_html()
you can use element.class#id syntax to wrap expressions in
HTML elements (all parts are optional). Let’s use this syntax to place
manufacturer and model in <strong> and
<em> elements, each with a custom class.
<ul>
```{epoxy_html, .data = mpg}
<li>
{{strong.car-make manufacturer}}
{{em.car-model model}}
</li>
```
</ul><ul>
```{=html}
<li>
<strong class="car-make">Chevrolet</strong><strong class="car-make">Dodge</strong><strong class="car-make">Ford</strong>
<em class="car-model">Malibu</em><em class="car-model">Caravan</em><em class="car-model">Expedition</em>
</li>
```
</ul>Because the epoxy_transform_html() transformer uses
.<class> to create
<span class="class"> elements,
epoxy_html() also recognizes @<inline>
to access the inline transformers. So
{{.uppercase manufacturer}} is assumed to be a CSS class
and not an inline transformer class.
```{=html}
<span class="uppercase">Chevrolet</span>
CHEVROLET
```Raw LaTeX chunks
Similarly, you can also use epoxy_latex chunks to epoxy
R and LaTeX together. Wrap expressions in these types of chunks with
<< and >>.
\begin{itemize}
```{epoxy_latex, .data = mpg}
\item <<.strong manufacturer>> <<.emph model>> gets <<cty>> city and <<hwy>> highway miles per gallon.
```
\end{itemize}In R Markdown knitting into a LaTeX output, this renders as:
\begin{itemize}
```{=latex}
\item \textbf{Chevrolet} \emph{Malibu} gets 19 city and 27 highway miles per gallon.
\item \textbf{Dodge} \emph{Caravan} gets 7 city and 24 highway miles per gallon.
\item \textbf{Ford} \emph{Expedition} gets 11 city and 17 highway miles per gallon.
```
\end{itemize}Note that, like epoxy_html chunks,
epoxy_latex places the output in raw
latex blocks. This behavior can be disabled by setting the chunk
option latex_raw = FALSE.
⚠️ Note: Prior to v1.0.0, epoxy used single
< and > characters for expression
delimiters in epoxy_latex() chunks. This can lead to subtle
but inescapable problems if you need to use these characters
inside your expression. As a result, epoxy_latex()
now uses << and >> to delimit
inline expressions.