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Generate Manual Table of Contents in (R)Markdown Documents
#' Render Table of Contents
#'
#' A simple function to extract headers from an RMarkdown or Markdown document
#' and build a table of contents. Returns a markdown list with links to the
#' headers using
#' [pandoc header identifiers](http://pandoc.org/MANUAL.html#header-identifiers).
#'
#' WARNING: This function only works with hash-tag headers.
#'
#' Because this function returns only the markdown list, the header for the
#' Table of Contents itself must be manually included in the text. Use
#' `toc_header_name` to exclude the table of contents header from the TOC, or
#' set to `NULL` for it to be included.
#'
#' @section Usage:
#' Just drop in a chunk where you want the toc to appear (set `echo=FALSE`):
#'
#' # Table of Contents
#'
#' ```{r echo=FALSE}
#' render_toc("/path/to/the/file.Rmd")
#' ```
#'
#' @param filename Name of RMarkdown or Markdown document
#' @param toc_header_name The table of contents header name. If specified, any
#' header with this format will not be included in the TOC. Set to `NULL` to
#' include the TOC itself in the TOC (but why?).
#' @param base_level Starting level of the lowest header level. Any headers
#' prior to the first header at the base_level are dropped silently.
#' @param toc_depth Maximum depth for TOC, relative to base_level. Default is
#' `toc_depth = 3`, which results in a TOC of at most 3 levels.
render_toc <- function(
filename,
toc_header_name = "Table of Contents",
base_level = NULL,
toc_depth = 3
) {
x <- readLines(filename, warn = FALSE)
x <- paste(x, collapse = "\n")
x <- paste0("\n", x, "\n")
for (i in 5:3) {
regex_code_fence <- paste0("\n[`]{", i, "}.+?[`]{", i, "}\n")
x <- gsub(regex_code_fence, "", x)
}
x <- strsplit(x, "\n")[[1]]
x <- x[grepl("^#+", x)]
if (!is.null(toc_header_name))
x <- x[!grepl(paste0("^#+ ", toc_header_name), x)]
if (is.null(base_level))
base_level <- min(sapply(gsub("(#+).+", "\\1", x), nchar))
start_at_base_level <- FALSE
x <- sapply(x, function(h) {
level <- nchar(gsub("(#+).+", "\\1", h)) - base_level
if (level < 0) {
stop("Cannot have negative header levels. Problematic header \"", h, '" ',
"was considered level ", level, ". Please adjust `base_level`.")
}
if (level > toc_depth - 1) return("")
if (!start_at_base_level && level == 0) start_at_base_level <<- TRUE
if (!start_at_base_level) return("")
if (grepl("\\{#.+\\}(\\s+)?$", h)) {
# has special header slug
header_text <- gsub("#+ (.+)\\s+?\\{.+$", "\\1", h)
header_slug <- gsub(".+\\{\\s?#([-_.a-zA-Z]+).+", "\\1", h)
} else {
header_text <- gsub("#+\\s+?", "", h)
header_text <- gsub("\\s+?\\{.+\\}\\s*$", "", header_text) # strip { .tabset ... }
header_text <- gsub("^[^[:alpha:]]*\\s*", "", header_text) # remove up to first alpha char
header_slug <- paste(strsplit(header_text, " ")[[1]], collapse="-")
header_slug <- tolower(header_slug)
}
paste0(strrep(" ", level * 4), "- [", header_text, "](#", header_slug, ")")
})
x <- x[x != ""]
knitr::asis_output(paste(x, collapse = "\n"))
}
---
title: "blogdown toc example"
author: '@gadenbuie'
date: "2/28/2018"
output: html_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
source("render_toc.R")
```
## Table of Contents {#crazy-slug-here}
```{r toc, echo=FALSE}
render_toc("blogdown-toc-example.Rmd")
```
### WONT BE INCLUDED IN TOC
# Writing
## R Markdown
This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.
When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:
```{r cars}
# This is not a header
summary(cars)
```
## Regular Code
```r
# Regular markdown code (not run)
ggplot(mtcars, aes(x = wt, y = mpg)) +
geom_point()
```
# Plots
## Including Plots {#plots-are-here .class-foo}
You can also embed plots, for example:
```{r pressure, echo=FALSE}
plot(pressure)
```
Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.
# More
## Level 1
### Level 1.a
#### Level 1.a.i
### Level 1.b
@datahua
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datahua commented May 27, 2022

Nice work! Wondering if there is anyway to change the color of the toc titles?

@manomuthus
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manomuthus commented Sep 21, 2022

Hi, this is a very useful function. Thanks. But is there a way to keep the original chapter numbers instead of bullets?

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