rmarkdown/bookdown: Edit `metadata$abstract` on the fly?

Question

This has partially been asked (without any takers) here and I have reached out via comment here - apologies for the multi-pronged approach ...

In my ongoing quest (see here for the example and further aspects) to automated report assembly using bookdown, I would like to do the following:

Start a paragraph in the yaml header like so:

---
title: "Test Doc"
author: "Balin"
date: "May 29, 2018"
abstract: "Bare bones abstract."
output: 
  bookdown::pdf_document2:
    toc: no
---

This stands in for an extensive report where `code`, its 
documentation and interpretation of its results are integrated:

1. We load some data:
   ```{r data-loading}
    my_data <- cars
    # PLACEHOLDER (see in text below) #
   ```
<!-- ... -->

As the processing progresses I aim to edit the yaml-deriving abstract, cumulatively assembling/augmenting it. I know about rmarkdown::metadata$abstract (see e.g. here), but the metadata object appears immutable and can't be edited.

I in essence want to replace the PLACEHOLDER bit in the example with something like:
```
rmarkdown::metadata$abstract <- paste(
  rmarkdown::metadata$abstract,
  "The analyzed dataset contains",
  nrow(my_data),
  "data points.")
```
Can that be achieved?

score 1 · Answer 1 · answered Jun 01 '18 at 19:04

Remember that the YAML doesn't have to be all in one block, or all at the beginning of your Rmarkdown document.

In my Rmarkdown reports I put the abstract in a separate YAML block after the analysis. At that point you can reference R objects as inline expressions as in other Rmarkdown. The abstract will still be placed a the beginning of the output document.

```{r last_chunk}
# run R code
````

---
abstract: |
On `r Sys.Date()` we analyzed `r nrow(mydata)` observations and found...
----

The only trick - you must have empty lines before and after the --- delimiters for the YAML block to be recognized.

Caveat - I use this in Rmarkdown but haven't tested it with bookdown.

rmarkdown/bookdown: Edit `metadata$abstract` on the fly?

1 Answers1