R in frontmatter with custom listing template

[nurfatimaj]

Hi!

I would like to create a listing item where some elements of the frontmatter depend on the output of R command like in the example below

---
title: "title"
authors: 
  - name: "`r rmarkdown::yaml_front_matter(list.files(params[['project-path']], 'index.Rmd', full.names = TRUE))$author`"

params:
    project-path: '~/project/'
---

That is, I have a separate project folder, where I have all my work and output relevant to that project. I would like quarto to access this information when rendering the website, to minimize duplication. The idea is to access this way abstract and all relevant pdf outputs without having to copy paste them manually.

I tried the above example and it works well when I am rendering that particular page.

But on the listing page, I get this

I am not sure, if there is a deeper issue why listings can't handle R code or is it an issue with my listing template. If latter, could you please let me know, how can I enable evaluation of R code in frontmatter yaml. Here is the portion of my template that prints the authors:

<div class="quarto-title-authors">
    <ul class="listing-author">
        <% for (const athr of item.authors) {%>
            <% if (athr.url) { %>
                <li><a href="<%- athr.url %>"><%- athr.name %></a></li>
            <% } else { %>
                <li><%- athr.name %></li>
            <% } %>
        <% } %>
    </ul>
</div>

Thank you!

[mcanouil]

To use R code in YAML, you have to use !expr prefix (see https://quarto.org/docs/computations/r.html#chunk-options).

But the issue might also be related to #1505.

[cscheid]

You need double quotes after !expr

This is incorrect syntax:

title: "!expr rmarkdown::yaml_front_matter(list.files(params[['project-path']], 'index.Rmd', full.names = TRUE))$title"
params:
  project-path: '~/project/'

This is the appropriate syntax:

title: !expr "rmarkdown::yaml_front_matter(list.files(params[['project-path']], 'index.Rmd', full.names = TRUE))$title"
params:
  project-path: '~/project/'

YAML is not intuitive, and more advanced uses like this will require unfortunately that you're comfortable with these sharper corners.

[nurfatimaj]

Thank you for a reply! I tried your suggestions and still doesn't work. I thought perhaps it's something wrong with my R function so I tried rendering the following dummy page

---
title: !expr "1+1"
editor: visual
---

And I keep getting this error: "ERROR: TypeError: title2.trim is not a function".

I tried also using as.character(1+1) in this dummy page, removing the quotes, quoting the entire thing including !expr, all with the same error above.

Does it work for you? If so, then perhaps I should reinstall quarto or something else? And just to be clear, the !expr works no problem when I use it in chunk options like so

{r}
#| fig.cap: !expr 1+1

hist(rnorm(1000))

[cscheid]

I apologize. !expr only appears to work inside r code cells, even though the knitr engine is the one running.

I don't know a clean way to do this in quarto.

[nurfatimaj]

I see. May I press a little more on this topic? So, the !expr doesn't work in the frontmatter, but this works

title: "`r 1+1`"

And to be more precise using the folder structure example above, it works when I render website/research/paperA/index.qmd file. Would you happen to know how can I make it work for rendering the listing page website/listing.qmd as well?

[mcanouil]

There was a Discussion about these constraints: #606 (comment)

[mcanouil]

Here is an alternative, which basically includes the yaml (everything or only few selected fields) from another document within the Quarto document.

---
format: html
params:
  project-path: "."
---

```{r}
#| output: asis
#| echo: false
cat(
  "---",
  yaml::as.yaml(
    rmarkdown::yaml_front_matter(
      input = list.files(
        path = params[["project-path"]],
        pattern = 'index.Rmd',
        full.names = TRUE
      )[c("title", "any_other_field")]
    )
  ),
  "---",
  sep = "\n"
)
```

[nurfatimaj]

Thank you! Unfortunately, it does not solve the issue with rendering the listing page, so for now I just have to remember to copy the yaml fields correctly. But I used your logic to copy other files that I want to include and link on the page. At least some automation 😊

[mcanouil]

Did you try to use ametadata.yml?

#1840 (comment)

https://quarto.org/docs/websites/website-listings-custom.html