Fuse multiple R Markdown documents to a single output file

This is a helper function to fuse() .Rmd files and convert all their Markdown output to a single output file, which is similar to bookdown::render_book(), but one major differences is that all HTML output is written to one file, instead of one HTML file per chapter.

Usage

fuse_book(input = ".", output = NULL, envir = parent.frame())

Arguments

input: A directory or a vector of file paths. By default, all .Rmd/.md files under the current working directory are used as the input, except for filenames that start with . or _ (e.g., _foo.Rmd), or .md files with the same base names as .Rmd files (e.g., bar.md will not be used if bar.Rmd exists). For a directory input, the file search will be recursive if input ends with a slash (i.e., sub-directories will also be searched). If a file named index.Rmd or index.md exists, it will always be treated as the first input file. Input files can also be specified in the config file _litedown.yml (in the input field under book).
output: An output file path or a filename extension (e.g., .html, .tex, .xml, .man, .markdown, or .txt). In the latter case, the output file path will use the extension on the same base filename as the input file if the input is a file. If output is not character (e.g., NA), the results will be returned as a character vector instead of being written to a file. If output is NULL or an extension, and the input is a file path, the output file path will have the same base name as the input file, with an extension corresponding to the output format. The output format is retrieved from the first value in the output field of the YAML metadata of the input (e.g., html will generate HTML output). The output argument can also take an output format name (possible values are html, latex, xml, man, commonmark, and text). If no output format is detected or provided, the default is HTML.
envir: An environment in which the code is to be evaluated. It can be accessed via fuse_env() inside fuse().

Value

An output file path or the output content, depending on the output argument.

Details

If the output format needs to be customized, the settings should be written in the config file _litedown.yml, e.g.,

---
output:
  html:
    options:
      toc:
        depth: 4
  latex:
    meta:
      documentclass: "book"

In addition, you can configure the book via the book field, e.g.,

---
book:
  new_session: true
  subdir: false
  pattern: "[.]R?md$"
  chapter_before: "Information before a chapter."
  chapter_after: "This chapter was generated from `$input$`."
---

The option new_session specifies whether to render each input file in the current R session or a separate new R session; chapter_before and chapter_after specify text to be added to the beginning and end of each file, respectively, which accepts some variables (e.g., $input$ is the current input file path).