Pass body of Rmarkdown chunk as argument to child document - r

Question

I've designed an expandable info box for my blog (which is rendered from Rmarkdown) which I want to use as a template.
At the momentan I just write more or less plain HTML in the main Rmarkdown document, as below:
<div class="info" markdown="1">
<details>
<summary class="info-header" markdown="1">
Title <i class="fas fa-info-circle"></i>
</summary>
<p class="info-details">
Here goes the body
</p>
</details>
</div>
With some CSS this renders nicely:
Ideally I would like to replace the HTML above by using some kind of child document which has a title argument to specify the title, and (and this is the tricky part) which passes the whole body of the Rmarkdown chunk to the body section of the child document. So ideally the above HTML could be written as.
```{r, child = "info_box.Rmd", title = "My Title"}
Here goes the body
```
Is this possible? I understand how to insert a child document, also with arguments, and when looking at rmarkdown::hmtl_document() I do get a glimpse of how the use real arguments like title, but can we pass the body of the Rmarkdown chunk down to the child so that it is used at a specific place? Do we need a custom output format for this and how would it look like?
Any help appreciated. I'm also open for other solutions, but it would be more than great if the ideal approach above would work.

Answer 1

I am giving another answer which is based on knitr output hooks and Pandoc Lua filter that also works fine for rmarkdown::html_document (and probably a better approach than the previous one).
Pass the child document path to the chunk option child_into_box and specify the box title to option box_title. One very important detail to note is that you must at least insert a comment in that chunk, otherwise for an empty chunk the redefined knitr source hook does not work.
---
title: Passing Child document Text to Info box.
output:
html_document:
pandoc_args:
- --lua-filter=box_wrap.lua
---
## Rmarkdown
Some text
```{r}
#| echo: false
library(knitr)
default_source_hook <- knit_hooks$get('source')
knit_hooks$set(
source = function(x, options) {
if(is.null(options$child_into_box))
default_source_hook(x, options)
else {
res <- knitr::knit_child(input = options$child_into_box, envir = environment(), quiet = TRUE)
div_start = paste0("::: {wrap-box=true box-title='", options$box_title, "'}")
paste0(div_start, "\n", unlist(res), "\n", "\n:::\n")
}
}
)
```
Some more text
```{r}
#| child_into_box: info_box.Rmd
#| box_title: my info test box
# comment
```
box_wrap.lua
local str = pandoc.utils.stringify
local template_info_box_p1 = [[
<div class="note" markdown="1">
<details>
<summary class="note-header" markdown="1">
%s<i class="fas fa-info-circle"></i>
</summary>
<div class="note-details">
]]
local template_info_box_p2 = [[
</div>
</details>
</div>
]]
function Div(el)
if el.attributes['wrap-box'] then
local title = str(el.attributes['box-title'])
local info_box = string.format(template_info_box_p1, title)
local info_box_rb1 = pandoc.RawBlock('html', info_box)
local info_box_rb2 = pandoc.RawBlock('html', template_info_box_p2)
el.content:insert(1, info_box_rb1)
el.content:insert(info_box_rb2)
return el
end
end

Answer 2

Since the output format is HTML, a possible solution based on pandoc lua filter and Javascript is as follows,
main.Rmd
---
title: Passing Child document Text to Info box.
output:
html_document:
includes:
after_body: infoBox.html
pandoc_args:
- --lua-filter=info_box.lua
---
## Rmarkdown
::: {.info-box title="My new Title" #first}
:::
::: {.add-to-info #first}
```{r}
#| child: info_box.Rmd
```
Also some random text to be inserted into that info box
:::
::: {.info-box title="More info box" #second}
:::
::: {.add-to-info #second}
```{r}
#| child: info_box.Rmd
```
Also some random text to be inserted into that info box
:::
So to add contents from child-document to the info box you need to do two thing.
Firstly, create a pandoc div (using :::) with class .info-box, give it title that you want and give a unique id (suppose, #first) so that we could use it to insert the content of a child document to this specific info box.
secondly, wrap the code chunk with the child option with another pandoc div associated with class .add-to-info and use the id of the info box to where you want the content of this child document to be.
Now following these two steps you can generate as many as info box you want.
info_box.Rmd
Lorem ipsum dolor sit amet, eget, etiam, a metus purus sit quisque elit, suscipit.
```{r}
1 + 1
```
```{r}
plot(1:10)
```
```{r}
head(mtcars)
```
(no need to use title or output for the child document, it simply contains the body text)
info_box.lua
local template_info_box_p1 = [[
<div class="info" markdown="1">
<details>
<summary class="info-header" markdown="1">
%s <i class="fas fa-info-circle"></i>
</summary>
<p class="info-details" id="%s">
]]
local template_info_box_p2 = [[
</p>
</details>
</div>
]]
function Div(el)
if el.classes:includes('info-box') then
local title = el.attributes['title']
local id = el.identifier
local info_box_p1 = string.format(template_info_box_p1, title, id)
local info_box_html_p1 = pandoc.RawBlock('html', info_box_p1)
local child_content = el.content
local info_box_html_p2 = pandoc.RawBlock('html', template_info_box_p2)
return pandoc.Div({info_box_html_p1, info_box_html_p2})
end
end
infoBox.html
<script>
function add_to_info() {
let childs = document.querySelectorAll("div.add-to-info");
let info_box = document.querySelectorAll('p.info-details');
childs.forEach(el => {
info_box.forEach(box => {
if (el.id === box.id) {
box.appendChild(el);
}
});
});
}
window.onload = add_to_info();
</script>
A portion of the rendered ouput
Note that, this output lacks the necessary CSS styles along with fontawesome icon, which you can handle accordingly using the embedded classes info-header and info-details.

Answer 3

I found a first answer looking at this SO post:
I could create a template info_box.Rmd like:
---
title: ""
output: rmarkdown::html_document
---
<div class="note" markdown="1">
<details>
<summary class="note-header" markdown="1">
`r title`<i class="fas fa-info-circle"></i>
</summary>
<p class="note-details">
`r body`
</p>
</details>
</div>
And then replace the intial HTML from my post with:
```{r, echo = FALSE, results='asis'}
title <- "My new Title"
body <- "The new body"
cat(
knitr::knit_child("info_box.Rmd",
envir = environment(),
quiet = TRUE)
)
```
And it works:
However, I'd still prefer a solution looking like this:
```{r, child = "info_box.Rmd", title = "My Title"}
Here goes the body
```