How to use htmltools::tagList such that headers show in RMarkdown table of contents

Question

I need to generate multiple htmlwidgets within a loop in an RMarkdown document. This is accomplished using htmltools::tagList. The following snippet will generate HTML output with 2 level 2 headings and a datatable in each section. The only problem is that I specified toc: true but though tags$h2(headers[i]) will render a level 2 headings on the page, those headings are not picked up by the table of contents. Is there a way get these headings in the TOC?

---
output: 
  html_document:
    toc: true
---

## level 2 heading 0 - this one in TOC

```{r}
library(DT)
library(htmltools)

headers <- c("level 2 heading 1", "level 2 heading 2")
html_tags <- vector(mode = "list", length = 2*length(headers))
for (i in 1:length(headers)) {
  html_tags[[(2*i)-1]] <- tags$h2(headers[i])
  html_tags[[(2*i)]] <- list(list(datatable(iris)))
}

tagList(html_tags)
```

Note that in the result below the heading generated using "##" shows up in the table of contents, but the headings from the tagList call, though they render correctly in the document, are now in the table of contents.

I cannot understand what you mean. Can you explain more? maybe you can check this page's code: stackoverflow.com/questions/43446523/… — Peter Chen
See edits above. Headings render correctly, but only show in table of contents if input outside of the tagList using "##" in markdown syntax — Matt Pollock

Peter Chen Peter Chen · Accepted Answer · 2017-04-26T02:55:37

Try this:

---
output: 
  html_document:
    toc: true
---
```{r, echo=FALSE, message=FALSE, warning=FALSE}
library(DT)
library(htmltools)
```
```{r ,include = FALSE}
DT::datatable(iris)
```
## level 2 heading 0 - this one in TOC

```{r echo=FALSE, message=FALSE, warning=FALSE, results = 'asis'}
for (i in 1:2){
  cat("  \n## level 2 heading", i, "  \n")
   print(htmltools::tagList(DT::datatable(iris)))
  cat("  \n")
}
```

And the result is:

Maybe this is what you actually want.

Remember: You should avoid headers <- c("level 2 heading 1", "level 2 heading 2").
If you need hundred or thousand of headers, this isn't efficient and must waste too much time.

How to use htmltools::tagList such that headers show in RMarkdown table of contents

1 Answers