Inserting a Page Break within a Code Chunk in RMarkdown (Converting to PDF)

In this post, we’ll explore how to insert page breaks within code chunks in RMarkdown documents that are converted to PDF using rmarkdown, pandoc, and knitr.

Introduction

RMarkdown is a powerful tool for creating documents that incorporate executable code chunks. When converting these documents to PDF, it’s often desirable to include page breaks between sections of the document, such as between plots or statistical output. However, inserting page breaks within a single code chunk can be tricky.

In this post, we’ll discuss how to achieve this using rmarkdown, pandoc, and knitr.

Background

RMarkdown documents are created using R code that is embedded in Markdown syntax. When converted to PDF, the document is rendered as a static HTML file, which is then printed to a PDF. The conversion process involves several steps:

1. R code is executed, producing output.
2. Pandoc renders the R code chunk into a string of text, including any plots or statistical output generated by the code.
3. Knitr writes this string to a temporary file.

During the writing phase, knitr uses the results='asis' option to include the rendered output in the document. This allows for dynamic formatting and layout changes within the document.

However, when trying to insert page breaks within a single code chunk, things become more complicated. Pandoc does not recognize the \newpage or \pagebreak commands as legitimate PDF control sequences.

Solution

To achieve our goal, we need to use results='asis' in conjunction with carefully managed line breaks and escape sequences for the page break commands.

Here’s a step-by-step guide on how to do this:

1. Reduce and Reproduce the Example

First, we’ll create a reduced and reproducible example that demonstrates our approach. We’ll use ggplot2 to generate some sample plots and rmarkdown for formatting.

# Load required libraries
library("ggplot2")
library("rmarkdown")

# Create a vector of batch values
Values <- c("Batch1", "Batch2", "Batch3")

# Loop over each value in the vector
for (v in Values) {
  # Read in a sample CSV file (assuming it's named 'data.csv')
  testR <- read.csv(file.path("data.csv"), header = T)
  
  # Generate a scatterplot of batches for v
  ggplot(testR, aes(x = Time, y = Value, color = Batch)) +
    geom_point(size = 3) + 
    xlab("Timepoint") + 
    ylab(v) + 
    scale_x_continuous(breaks = seq(0, 60, by = 6)) + 
    ggtitle(paste("Scatterplot of Batches for ", v, sep = ""))
  
  # Save the plot as a JPEG
  ggsave(paste(v, "__", "Scatterplot of Batches for ", v, ".jpeg", sep = ""), width = 8, height = 6)
  
  # Print the page break command followed by line breaks
  cat("\n\n\\pagebreak\n")
  writeLines("ValueForV")
}

2. Add results='asis' to the R Chunk

Next, we’ll modify our R code chunk to include results='asis'. This will allow us to include the rendered output within the document.

---
title: "test"
output: pdf_document
---

```{r, echo=FALSE, results='asis'}
for (i in 1:3) {
  print(ggplot2::qplot(i, i+1))
  cat("\n\n\\pagebreak\n")
  writeLines("ValueForV")
}

In this example, we’ve added the results='asis' option to our R code chunk. This tells knitr to include the rendered output in the document.

3. Escape Page Break Commands

To avoid any issues with special characters or syntax errors when using page breaks within a single code chunk, it’s essential to escape these commands.

---
title: "test"
output: pdf_document
---

```{r, echo=FALSE, results='asis'}
for (i in 1:3) {
  print(ggplot2::qplot(i, i+1))
  cat("\n\n\\newpage\n")
  writeLines("ValueForV")
}

By escaping the \newpage command with a backslash (\) before it is used, we ensure that pandoc recognizes it as a legitimate PDF control sequence.

Conclusion

Inserting page breaks within a single code chunk in RMarkdown documents can be challenging. By using results='asis', carefully managed line breaks, and escape sequences for the page break commands, you can achieve your goal and maintain clean formatting throughout your document.

I hope this helps! Let me know if you have any questions or need further clarification on any of the steps.

Last modified on 2024-09-26