R function to double-render a R Markdown document destined to be a Beamer presentation. Solves the total frame number issue.

render-beamer.R

render_beamer <- function(input = NULL, cleanup = FALSE, ...){
  assertthat::assert_that(fs::file_exists(input))
  
  bare_input <- fs::path_ext_remove(input)
  out_dir <- fs::path_dir(input)
  
  rmarkdown::render(input, ...)
  
  pre_dir <- rbind(tibble::enframe(fs::dir_ls(out_dir)),
           glue::glue('{fs::as_fs_path(bare_input)}.pdf'),
           glue::glue('{fs::as_fs_path(bare_input)}.tex'))
  
  if(!fs::file_exists(glue::glue('{bare_input}.tex'))){
    stop('You must keep the TeX file after knitting your Rmd.')
  }
  
  tex_engine <- getOption('latex.engine', default = Sys.which('pdflatex'))
  
  system(glue::glue('{tex_engine} --output-directory={out_dir} {bare_input}.tex'))
  system(glue::glue('{tex_engine} --output-directory={out_dir} {bare_input}.tex'))
  
  if(cleanup){
    post_dir <- tibble::enframe(fs::dir_ls(out_dir))
    to_remove <- dplyr::anti_join(post_dir, pre_dir, by = 'value')
    fs::file_delete(to_remove$value)
  }
  
  if(Sys.info()[1] %in% 'Windows'){
    system(glue::glue('start {bare_input}.pdf'))
  } else {
    system(glue::glue('open {bare_input}.pdf'))
  }
}