You probably know that you can include a child document in a knitr document
(such as R Markdown) via the chunk option child. If you do not, you may see
Section 16.4 of the R Markdown
Cookbook.
You may also know that you can convert an R script to R Markdown via the
function knitr::spin(). Again, if you do not, you may read Section
3.3 of the book.
Then the question is, when you render an R Markdown document, can you spin a
child script inside that document? Tom asked this
question on Stack Overflow last
month, and the answer is “Yes.” There is a function knitr::spin_child()
designed exactly for this purpose. When you call this function inside an R code
chunk, it spins an R script to R Markdown, and includes the R Markdown document
as a child document of the main document. For example, if you have an R script
test.R:
#' # This is a child document
1 + 1
You can convert it to a child R Markdown document inside the main document:
---
title: The main document
---
```{r, echo=FALSE}
knitr::spin_child('test.R')
```
When you knit the main document above, you are essentially knitting this document below:
---
title: The main document
---
# This is a child document
```{r}
1 + 1
```
In conclusion, knitr::spin_child() enables you to write a part of your
report with an R script, if you do not want to write the whole report in an R
script.