Template Engine Inspired by 'Jinja'

Template engine powered by the 'inja' C++ library. Users write a template document, using syntax inspired by the 'Jinja' Python package, and then render the final document by passing data from R. The template syntax supports features such as variables, loops, conditions and inheritance.

jinjar

jinjar is a templating engine for R, inspired by the Jinja Python package and powered by the inja C++ library.

Installation

You can install the released version of jinjar from CRAN with:

install.packages("jinjar")

Or you can install the development version from GitHub:

# install.packages("remotes")
remotes::install_github("davidchall/jinjar")

Usage

library(jinjar)

render("Hello {{ name }}!", name = "world")
#> [1] "Hello world!"

Here’s a more advanced example using loops and conditional statements. The full list of supported syntax is described in vignette("template-syntax").

template <- 'Humans of A New Hope

{% for person in people -%}
{% if "A New Hope" in person.films and default(person.species, "Unknown") == "Human" -%}
* {{ person.name }} ({{ person.homeworld }})
{% endif -%}
{% endfor -%}
'

template |>
  render(people = dplyr::starwars) |>
  writeLines()
#> Humans of A New Hope
#> 
#> * Luke Skywalker (Tatooine)
#> * Darth Vader (Tatooine)
#> * Leia Organa (Alderaan)
#> * Owen Lars (Tatooine)
#> * Beru Whitesun Lars (Tatooine)
#> * Biggs Darklighter (Tatooine)
#> * Obi-Wan Kenobi (Stewjon)
#> * Wilhuff Tarkin (Eriadu)
#> * Han Solo (Corellia)
#> * Wedge Antilles (Corellia)
#> * Raymus Antilles (Alderaan)

Related work

An important characteristic of a templating engine is how much logic is supported. This spectrum ranges from logic-less templates (i.e. only variable substitution is supported) to arbitrary code execution. Generally speaking, logic-less templates are easier to maintain because their functionality is so restricted. But often the data doesn’t align with how it should be rendered – templating logic offers the flexibility to bridge this gap.

Fortunately, we already have very popular R packages that fall on opposite ends of this spectrum:

• whisker – Implements the Mustache templating syntax. This is nearly logic-less, though some simple control flow is supported. Mustache templates are language agnostic (i.e. can be rendered by other Mustache implementations).
• knitr and rmarkdown – Allows arbitrary code execution to be knitted together with Markdown text content. It even supports multiple language engines (e.g. R, Python, C++, SQL).

In contrast, jinjar strikes a balance inspired by the Jinja Python package. It supports more complex logic than whisker, but without the arbitrary code execution of knitr.