Programmatically add tags to yaml header during knitting R markdown file

Question

I'd like to programmatically add tags to the YAML header of a blogdown post when clicking the "knit" button.

For example something like this:

---
title: This is a post
author: brshallo
date: '2022-02-11'
tags: "`r stringr::str_c('\n  - ', stringr::str_flatten(c('rstats', 'datascience'), '\n  - '))`"
slug: this-is-a-post
---

Related Resources

I've tried a variety of solutions with !r, !expr, and iterations on these but so far no luck.

Here are some related threads:

• Importing common YAML in rstudio/knitr document
• How to edit an R markdown YAML header programmatically?
• https://community.rstudio.com/t/is-there-a-way-to-specify-a-nested-group-of-params-in-rmarkdown-yaml-if-not-should-there-be/117393/2
• https://community.rstudio.com/t/rmarkdown-list-in-yaml/94147/5
• packages: ymlthis and yaml
• context: blogdown#647

I'd at first assumed this was a more general rmarkdown problem rather than blogdown specific but given that some of the solutions mentioned in threads above seemed to work when inputting generic params I wasn't sure...

Answer 1

To generate a valid YAML array, you could use the alternative syntax [ ], e.g.,

tags: ["`r paste(head(letters), collapse = '", "')`"]

which generates:

tags: ["a", "b", "c", "d", "e", "f"]

Note the hack collapse = '", "': since there already exists a pair of double quotes outside the R expression, you should only generate the part a", "b", "c", "d", "e", "f from the R expression.

-- solution copied from Yihui's explanation at blogdown#647