Skip to contents

These transformers provide additional automatic formatting for the template strings. They are designed to be used with the .transformer chunk option of in epoxy chunks. You can use epoxy_transform() to chain several transformers together. epoxy_transform() and individual epoxy transform functions can be used in epoxy, epoxy_html and epoxy_latex chunks and will choose the correct engine for each.


epoxy_transform(..., engine = NULL, syntax = lifecycle::deprecated())

epoxy_transform_get(engine = c("md", "html", "latex"), inline = FALSE)

epoxy_transform_set(..., engine = NULL, syntax = lifecycle::deprecated())



Transformer functions, e.g. epoxy_transform_bold or the name of an epoxy transform function, e.g. "bold", or a call to a transform function, e.g. epoxy_transform_bold(). epoxy_transform() chains the transformer functions together, applying the transformers in order from first to last.

For example, epoxy_transform("bold", "collapse") results in replaced strings that are emboldened and then collapsed, e.g. **a** and **b**. On the other hand, epoxy_transform("collapse", "bold") will collapse the vector and then embolden the entire string.

In epoxy_transform_apply(), the ... are passed to the underlying call the underlying function call.

In epoxy_transform_collapse(), the ... are ignored.


One of "markdown" (or "md"), "html", or "latex". The default is chosen based on the engine of the chunk where the transform function is called, or according to the option epoxy.engine. Caution: invalid options are silently ignored, falling back to "markdown".


[Deprecated] Use engine instead.


In epoxy_transform_get(), whether to return the session-specific inline formatting functions for epoxy_transform_inline().


A function of text and envir suitable for the .transformer argument of glue::glue().


  • epoxy_transform(): Construct a chained transformer using epoxy transformers for use as a glue transformer. The resulting transformers can be passed to the .transformer argument of epoxy() or glue::glue().

  • epoxy_transform_get(): Get the default epoxy .transformer for all epoxy engines or for a subset of engines.

  • epoxy_transform_set(): Set the default epoxy .transformer for all epoxy engines or for a subset of engines.

Output-specific transformations

The epoxy_transform_ functions will attempt to use the correct engine for transforming the replacement text for markdown, HTML and LaTeX. This choice is driven by the chunk engine where the transformer function is used. The epoxy engine corresponds to markdown, epoxy_html to HTML, and epoxy_latex to LaTeX.

Automatic engine selection only works when the epoxy transform functions are used with epoxy knitr engines and during the knitr rendering process. When used outside of this context, you can choose the desired engine by setting the engine to one of "markdown", "html" or "latex".

Session-wide settings

To change the transformer used by epoxy() and the HTML and LaTeX variants, use epoxy_transform_set(). This function takes the same values as epoxy_transform(), but makes them the default transformer for any epoxy() calls that do not specify a transformer. By default, the setting is made for all engines, but you can specify a single engine with the engine argument.

Here's a small example that applies the bold and collapse transformers to all epoxy chunks:

epoxy_transform_set("bold", "collapse")

Most often, you'll want to to update the default transformer to customize the formatting functions used by the inline transformer. You can use epoxy_transform_set() to change settings of existing formatting functions or to add new one. Pass the new function to an argument with the dot-prefixed name.

In the next example I'm setting the .dollar transformation to use "K" and "M" to abbreviate large numbers. I'm also adding my own transformation that truncates long strings to fit in 8 characters.

  .dollar = scales::label_dollar(
    accuracy = 0.01,
    scale_cut = scales::cut_short_scale()
  .trunc8 = function(x) glue::glue_collapse(x, width = 8)

epoxy("{.dollar 12345678}")
#> $12.34M
epoxy("{.trunc8 12345678}")
#> 12345...

Note that the engine argument can be used even with inline tranformations, e.g. to apply a change only for HTML you can use engine = "html".

To unset the session defaults, you have two options:

  1. Unset everything by passing NULL to epoxy_transform_set():

  2. Unset a single inline transformation by passing rlang::zap() to the named argument:

    epoxy_transform_set(.dollar = rlang::zap())

Or you can provide new values to overwrite the current settings. And as before, you can unset session defaults for a specific engine.

See also

Other epoxy's glue transformers: epoxy_transform_html(), epoxy_transform_inline()


epoxy("{.strong {.and letters[1:3]}}")
#> **a, b, and c**
epoxy("{.and {.strong letters[1:3]}}")
#> **a**, **b**, and **c**

# If you used the development version of epoxy, the above is equivalent to:
epoxy("{letters[1:3]&}", .transformer = epoxy_transform("bold", "collapse"))
#> **a**, **b**, and **c**
epoxy("{letters[1:3]&}", .transformer = epoxy_transform("collapse", "bold"))
#> **a, b, and c**

# In an epoxy_html chunk...
epoxy_html("{{.strong {{.or letters[1:3]}} }}")
#> <span class="strong">a, b, or c</span>

# Or in an epoxy_latex chunk...
epoxy_latex("<<.and <<.strong letters[1:3]>> >>")
#> \textbf{a}, \textbf{b}, and \textbf{c}

# ---- Other Transformers ----

# Format numbers with an inline transformation
amount <- 123.4234234
epoxy("{.number amount}")
#> 123
  "{.number amount}",
  .transformer = epoxy_transform_inline(
    .number = scales::label_number(accuracy = 0.01)
#> 123.42

# Apply _any_ function to all replacements
  "{amount} is the same as {amount}",
  .transformer = epoxy_transform_apply(round, digits = 0)
#> 123 is the same as 123

  "{amount} is the same as {amount}",
  .transformer = epoxy_transform(
    epoxy_transform_apply(~ .x * 100),
    epoxy_transform_apply(round, digits = 2),
    epoxy_transform_apply(~ paste0(.x, "%"))
#> 12342.34% is the same as 12342.34%