How to Combine Two RMarkdown (.Rmd) Files into a Single Output?

RMarkdown is a powerful tool that combines code and narrative text to create dynamic reports. In some scenarios, you might need to combine multiple RMarkdown files into a single document. This is especially useful when working on large projects where content is modularized across different .Rmd files. Thankfully, the knitr package provides a seamless way to achieve this using the knitr::include() function and the child option.

Here’s a step-by-step guide to combining two .Rmd files into a single output using R:

Step 1: Create Your First .Rmd File

Write the content for your first .Rmd file and save it using the following code:

first_content <- "
---
title: 'First Rmd File'
output: html_document
---

## This is the first Rmd file
Some content for the first file.
"
writeLines(first_content, 'first_file.Rmd')

This creates a file named first_file.Rmd with a simple structure.

Step 2: Create Your Second .Rmd File

Similarly, create the second .Rmd file in another cell:

second_content <- "
---
title: 'Second Rmd File'
output: html_document
---

## This is the second Rmd file
Some content for the second file.
"
writeLines(second_content, 'second_file.Rmd')

This saves the second .Rmd file as second_file.Rmd.

Step 3: Combine the Two Files

Using the knitr package, you can combine the contents of both .Rmd files into a single .Rmd file:

library(knitr)

# Define the paths to your two Rmd files
file1 <- "first_file.Rmd"
file2 <- "second_file.Rmd"

# Combine the contents of the two files
combined <- c(readLines(file1), readLines(file2))

# Write the combined content to a new Rmd file
writeLines(combined, "combined_file.Rmd")

This creates a new file called combined_file.Rmd containing the merged content of first_file.Rmd and second_file.Rmd.

Step 4: Render the Combined .Rmd File

To render the combined .Rmd file into a desired output format (e.g., HTML), use the rmarkdown::render() function:

library(rmarkdown)
render('combined_file.Rmd')

Output:

processing file: combined_file.Rmd
output file: combined_file.knit.md
Output created: combined_file.html

This generates an HTML file from the combined content, allowing you to preview the merged output.

Advantages of Using knitr for Combining .Rmd Files

• Modularity: Keep sections of your project in separate .Rmd files and combine them when needed.
• Dynamic Rendering: The combined file reflects updates made to individual .Rmd files.
• Ease of Use: The knitr::include() function and child option streamline the process.