Producing headings in Word files programmatically using knitr

I love knitr. Sometimes I have to send people documents in Word. It works beautifully except when I want to produce headings programmatically in code using cat(). This is fine in HTML:

sapply(headings, function(x){
    
  cat(paste0("<h1>", x, "</h1>"))
    
  cat(paste0("<p>", rep("Some text here", 10), "</p>"))
    
})

However, when writing Word .docx files using Rmarkdown the heading tags are not recognised. Well, they’re not printed, so they obviously are recognised, but they don’t work.

I’ve struggled for a long time to understand how to produce headings in Rmarkdown and to be honest in the past I’ve actually done it with a lot of guesswork and some silly hacky unnecessary code. Today I have finally figured out a foolproof way to do it very easily every time, so I present the whole document to you and to my future self when I inevitably forget how to do it:

---
title: "Minimal example"
author: "Chris Beeley"
date: "1 September 2015"
output: word_document
---

```{r setup, include=FALSE}

knitr::opts_chunk$set(echo = TRUE)

```


```{r, results = 'asis', echo = FALSE}

headings = letters[1:4]

invisible(
  
  sapply(headings, function(x){
    
    cat(paste0("#", x, "\n"))
    
    cat(paste0("<p>", rep("Some text here", 10), "</p>"))
    
  })
)

```

That’s it! Don’t forget the invisible() because otherwise if you use lists and things like that you’ll get the names of the list at the end.