Who is this aimed at?

We aim this document at anyone writing manuscripts and using R, including those who…

1. …collaborate with people who use Word
2. …want to write complex equations
3. …want to be able to change bibliography styles with less hassle
4. …want to spend more time actually doing research!

Why write reproducible papers?

Cool, thanks for sticking with us and reading up through here!

There are three reasons to write reproducible papers. To be right, to be reproducible, and to be efficient. There are more, but these are convincing to us. In more depth:

1. To avoid errors. Using an automated method for scraping APA-formatted stats out of PDFs, @nuijten2016 found that over 10% of p-values in published papers were inconsistent with the reported details of the statistical test, and 1.6% were what they called “grossly” inconsistent, e.g. difference between the p-value and the test statistic meant that one implied statistical significance and the other did not. Nearly half of all papers had errors in them.

2. To promote computational reproducibility. Computational reproducibility means that other people can take your data and get the same numbers that are in your paper. Even if you don’t have errors, it can still be very hard to recover the numbers from published papers because of ambiguities in analysis. Creating a document that literally specifies where all the numbers come from in terms of code that operates over the data removes all this ambiguity.

3. To create spiffy documents that can be revised easily. This is actually a really big neglected one for us. At least one of us used to tweak tables and figures by hand constantly, leading to a major incentive never to rerun analyses because it would mean re-pasting and re-illustratoring all the numbers and figures in a paper. That’s a bad thing! It means you have an incentive to be lazy and to avoid redoing your stuff. And you waste tons of time when you do. In contrast, with a reproducible document, you can just rerun with a tweak to the code. You can even specify what you want the figures and tables to look like before you’re done with all the data collection (e.g., for purposes of preregistraion or a registered report).

Learning goals

By the end of this class you should:

• Know what Markdown is and how the syntax works,
• See how to integrate code and data in RMarkdown,
• Understand the different output formats from RMarkdown and how to generate them, and
• Know about generating APA format files with papaja and bibtex.

Header

Headers in RMarkdown files contain some metadata about your document, which you can customize to your liking. Below is a simple example that purely states the title, author name(s), date, and output format.

---
title: "Untitled"
author: "NAME"
date: "July 28, 2017"
output: html_document
---

ProTip: The header is written in “YAML”, which means “yet another markup language.” You don’t need to know that, and don’t worry about it. Just make sure you are careful with indenting, as YAML does care about that.

For now, go ahead and set html_document to word_document, except if you have strong preferences for HTML or PDF.11 Note: to create PDF documents you also need a TeX installation. Don’t know what that is? You probably don’t have it then. More info below.

Body text

The body of the document is where you actually write your reports. This is primarily written in the Markdown format, which is explained in the Markdown syntax section.

The beauty of RMarkdown is, however, that you can evaluate R code right in the text. To do this, you start inline code with `r, type the code you want to run, and close it again with a `. Usually, this key is below the escape (ESC) key or next to the left SHIFT button.

For example, if you want to have the result of 48 times 35 in your text, you type ` r 48-35`, which returns 13. Please note that if you return a value with many decimals, it will also print these depending on your settings (for example, 3.1415927).

Code chunks

In the section above we introduced you to running code inside text, but often you need to take several steps in order to get to the result you need. And you don’t want to do data cleaning in the text! This is why there are code chunks. A simple example is a code chunk loading packages.

First, insert a code chunk by going to Code->Insert code chunk or by pressing CTRL+ALT+I. Inside this code chunk you can then type for example, library(ggplot2) and create an object x.

library(ggplot2)

x <- 1 + 1

If you do not want to have the contents of the code chunk to be put into your document, you include echo=FALSE at the start of the code chunk. We can now use the contents from the above code chunk to print results (e.g., \(x=2\)).

These code chunks can contain whatever you need, including tables, and figures (which we will go into more later). Note that all code chunks regard the location of the RMarkdown as the working directory, so when you try to read in data use the relative path in.

Exercises

Swap over to your new sample markdown.

1. Outlining using headings is a really great way to keep things organized! Try making a bunch of headings, and then recompiling your document.
2. Add a table of contents. This will involve going to the header of the document (the YAML), and adding some options to the html document bit. You want it to look like this (indentation must to be correct):

output: 
  html_document:
    toc: true

Now recompile. Looks nice, right?22 Pro-tip: you can specify how deep the TOC should go by adding toc_depth: 2 to go two levels deep

3. Try adding another option: toc_float: true. Recompile – super cool. There are plenty more great output options that you can modify. Here is a link to the documentation.

Headers

We’re going to want more libraries loaded (for now we’re loading them inline).

library(knitr)
library(ggplot2)
library(broom)
library(devtools)

We often also add chunk options to each code chunk so that, for example:

• code does or doesn’t display inline (echo setting)
• figures are shown at various sizes (fig.width and fig.height settings)
• warnings and messages are suppressed (warning and message settings)
• computations are cached (cache setting)

There are many others available as well. Caching can be very helpful for large files, but can also cause problems when there are external dependencies that change. An example that is useful for manuscripts is:

opts_chunk$set(fig.width=8, fig.height=5, 
               echo=TRUE, 
               warning=FALSE, message=FALSE, 
               cache=TRUE)

Graphs

It’s really easy to include graphs, like this one. (Using the mtcars dataset that comes with ggplot2).

qplot(hp, mpg, col = factor(cyl), data = mtcars)

All you have to do is make the plot and it will render straight into the text.

External graphics can also be included, as follows:

knitr::include_graphics("path/to/file")

Tables

There are many ways to make good-looking tables using RMarkdown, depending on your display purpose.

• The knitr package (which powers RMarkdown) comes with the kable function. It’s versatile and makes perfectly reasonable tables. It also has a digits argument for controlling rounding.

• For HTML tables, there is the DT package, which provides datatable – these are pretty and interactive javascript-based tables that you can click on and search in. Not great for static documents though.

• For APA manuscripts, it can also be helpful to use the xtable package, which creates very flexible LaTeX tables. These can be tricky to get right but they are completely customizable provided you want to google around and learn a bit about tex.

We recommend starting with kable:

kable(head(mtcars), digits = 1)

	mpg	cyl	disp	hp	drat	wt	qsec	vs	am	gear	carb
Mazda RX4	21.0	6	160	110	3.9	2.6	16.5	0	1	4	4
Mazda RX4 Wag	21.0	6	160	110	3.9	2.9	17.0	0	1	4	4
Datsun 710	22.8	4	108	93	3.8	2.3	18.6	1	1	4	1
Hornet 4 Drive	21.4	6	258	110	3.1	3.2	19.4	1	0	3	1
Hornet Sportabout	18.7	8	360	175	3.1	3.4	17.0	0	0	3	2
Valiant	18.1	6	225	105	2.8	3.5	20.2	1	0	3	1

Statistics

It’s also really easy to include statistical tests of various types.

For this, an option is the broom package, which formats the outputs of various tests really nicely. Paired with knitr’s kable you can make very simple tables in just a few lines of code.

mod <- lm(mpg ~ hp + cyl, data = mtcars)
kable(tidy(mod), digits = 3)

term	estimate	std.error	statistic	p.value
(Intercept)	36.908	2.191	16.847	0.000
hp	-0.019	0.015	-1.275	0.213
cyl	-2.265	0.576	-3.933	0.000

Of course, cleaning these up can take some work. For example, we’d need to rename a bunch of fields to make this table have the labels we wanted (e.g., to turn hp into Horsepower).

We often need APA-formatted statistics. We can compute them first, and then print them inline.

ts <- with(mtcars,t.test(hp[cyl==4], hp[cyl==6]))

There’s a statistically-significant difference in horsepower for 4- and 6-cylinder cars (\(t(11.49) = -3.56\), \(p = 0.004\)).

To insert these stats inline I wrote e.g. round(ts$parameter, 2) inside an inline code block.33 APA would require omission of the leading zero. papaja::printp() will let you do that, see below.

Note that rounding can occasionally get you in trouble here, because it’s very easy to have an output of \(p = 0\) when in fact \(p\) can never be exactly equal to 0. Nonetheless, this can help you prevent rounding errors and the wrath of statcheck.

Exercises

1. Using the mtcars dataset, insert a table and a graph of your choice into the document.44 If you’re feeling uninspired, try hist(mtcars$mpg).

Software requirements

To use papaja, make sure you are using the latest versions of R and RStudio. If you want to create PDF- in addition to DOCX-files you need TeX 2013 or later. Try MikTeX for Windows, MacTeX for Mac, or TeX Live for Linux. Some Linux users may need a few additional TeX packages for the LaTeX document class apa6 to work.55 For Ubuntu, we suggest running: sudo apt-get install texlive texlive-publishers texlive-fonts-extra texlive-latex-extra texlive-humanities lmodern.

Installing papaja

papaja has not yet been released on CRAN but you can install it from GitHub.

# Install devtools package if necessary
if(!"devtools" %in% rownames(installed.packages())) install.packages("devtools")

# Install papaja
devtools::install_github("crsh/papaja")

Creating a document

The APA manuscript template should now be available through the RStudio menus when creating a new R Markdown file.

When you click RStudio’s Knit button papaja, rmarkdown, and knitr work together to create an APA conform manuscript that includes both your manuscript text and the results of any embedded R code.

Note, if you don’t have TeX installed on your computer, or if you would like to create a Word document replace output: papaja::apa6_pdf with output: papaja::apa6_word in the document YAML header.

papaja provides some rendering options that only work if you use output: papaja::apa6_pdf. figsintext indicates whether figures and tables should be included at the end of the document—as required by APA guidelines—or rendered in the body of the document. If figurelist, tablelist, or footnotelist are set to yes a list of figure captions, table captions, or footnotes is given following the reference section. lineno indicates whether lines should be continuously numbered through out the manuscript.

Bibiographic management

It’s also possible to include references using bibtex, by using @ref syntax. An option for managing references is bibdesk, which integrates with google scholar.66 But many other options are possible.

With a bibtex file included, you can refer to papers. As an example, @nuijten2016 results in the in text citation “@nuijten2016”, or cite them parenthetically with [@nuijten2016] [@nuijten2016]. Take a look at the papaja APA example to see how this works.

citr is an R package that provides an easy-to-use RStudio addin that facilitates inserting citations. The addin will automatically look up the Bib(La)TeX-file(s) specified in the YAML front matter. The references for the inserted citations are automatically added to the documents reference section.

Once citr is installed (install.packages("citr")) and you have restarted your R session, the addin appears in the menus and you can define a keyboard shortcut to call the addin.

Exercise

Make sure you’ve got papaja, then open a new template file. Compile this document, and look at how awesome it is. (To compile you need texlive, a library for compiling markdown to PDF, so you may need to wait and install this later if it’s not working).

Try pasting in your figure and table from your other RMarkdown (don’t forget any libraries you need to make it compile). Presto, ready to submit!

For a bit more on papaja, check out this guide.