Generate table of contents from the yaml header title of a list of R Markdown files

Question

Is there a way to generate a list of the yaml header titles from a list of R Markdown files with the means of R? Suppose you have two files

A.Rmd

---
title: Titel of first file
---

B.Rmd

---
title: Titel of second file
---

Then the list should look like

File |Title
-----|--------------------
A.Rmd|Titel of first file
B.Rmd|Titel of second file

Could this list be generated as R Markdown file too - preferable with links to the original files?

score 2 · Answer 1 · answered Sep 26 '16 at 13:37

2

Here is a small and handy function, which gives you the title and the filename:

read_RMD_titles <- function(files){

  names_list <- lapply(1:length(files), function(x){

   title <- readLines(files[x])[2] 

    return(c(files[x], title))

  })

  return(unlist(names_list))  

}

read_RMD_titles(files = c("A.Rmd", "B.Rmd"))
# [1] "A.Rmd" "title: \"Untitled\""                      
# [3] "B.Rmd" "title: \"Untitled\""

You can modify this approach to your own needs now. This should be a starting point.

answered Sep 26 '16 at 13:37

J_F

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This is a starting point: what about titles which are wrapped onto the next line? – Claude Sep 26 '16 at 13:51
1

Thanks to this answer I have modified the function [read_RMD_titles](http://stackoverflow.com/a/39705496/2107731) – Claude Sep 26 '16 at 14:29
Nice, that you have found a solution for your needs! – J_F Sep 26 '16 at 14:30
Just found this `rmarkdown:::parse_yaml_front_matter(readLines(file))$title` – Claude Sep 26 '16 at 14:42

score 0 · Accepted Answer · edited May 23 '17 at 10:27

Thanks to the answer from J_F I modified his/her function as follows:

read_RMD_titles <- function(files){  
  names_list <- lapply(files, function(file) {
    lines = readLines(file)
    headerIdx = grep("^---\\s*$",lines)
    title = ""
    if (2 <= length(headerIdx)) {
      titleIdx = grep("^title:",lines[c(headerIdx[1]:headerIdx[2])])
      if (1 <= length(titleIdx)) {
        title = trimws(sub("^title:\\s*", "", lines[headerIdx[1] + titleIdx[1] - 1]))
        for (i in c(headerIdx[1] + titleIdx[1]:headerIdx[2])) {
          if (0 < regexpr("^\\s{2,}", lines[i])) {
            title = paste(title, trimws(lines[i]))
          } else {
            break
          }
        }
      }
    }
    return (c(file,title))
  })

  return(unlist(names_list))
}

If you like this please vote on his/her answer.

... or thanks to the answer to another question:

rmarkdown:::parse_yaml_front_matter(readLines(file))$title

might by used.

Generate table of contents from the yaml header title of a list of R Markdown files

2 Answers2