Literate programming

Overview

Teaching: 30 min
Exercises: 10 min

Questions

What tools are available to easily disseminate our work?

How can we make our work more reproducible?

Objectives

Learn the basics of RMarkdown and knitr

Learn to integrate R code with text and images.

2. Literate programming

Organize your work

make work more pleasant for yourself? (less tedium, less manual, less …)

reduce friction for collaboration?

reduce friction for communication?

make your work navigable, interpretable, and repeatable by others?

Getting the analysis right is only one link

Process, packaging, and presentation are often the weak links in the chain.

Markdown

What is Markdown?

Markdown is a particular type of markup language. Markup languages are designed to produce documents from plain text.
You may be familiar with LaTeX, another (though less human friendly) text markup language.
Tools render markdown to different formats (for example, HTML/pdf/Word).
- The main tool for rendering Markdown is pandoc.

Adapted from Carson Sievert’s markdown slides

Markdown enables fast publication to the web

Markdown Easy to write and read in an editor.
HTML Easy to publish and read on web.

Markdown versus HTML code

This is a Markdown document.

## Medium header 

It's easy to do *italics* or __make things bold__.

> All models are wrong, but some are useful. An approximate answer to the right problem is worth a good deal more than an exact answer to an approximate problem.

Code block below. Just affects formatting here.

```
x <- 3 * 4
```

I can haz equations. Inline equations, such as the average is computed as $\frac{1}{n} \sum_{i=1}^{n} x_{i}$. Or display equations like this:


$$
\begin{equation*}
|x|=
\begin{cases} x & \text{if $x\ge 0$,} \\\\
-x &\text{if $x\lt 0$.}
\end{cases}
\end{equation*}
$$


<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Title</title>
<!-- MathJax scripts -->
<script type="text/javascript" src="..."></script>
<style type="text/css">
body {
   font-family: Helvetica, arial, sans-serif;
   font-size: 14px;
...
</style>
</head>
<body>
<p>This is a Markdown document.</p>

<h2>Medium header</h2>

<p>It's easy to do <em>italics</em> or <strong>make things bold</strong>.</p>

<blockquote><p>All models are wrong, but some are...</p></blockquote>

<p>Code block below. Just affects formatting here.</p>

<pre><code>x <- 3 * 4</code></pre>

Markdown versus rendered HTML


This is a Markdown document.

## Medium header 

It's easy to do *italics* or __make things bold__.

> All models are wrong, but some are useful. An approximate answer to the right problem is worth a good deal more than an exact answer to an approximate problem.

Code block below. Just affects formatting here.


```r
x <- 3 * 4
```

I can haz equations. Inline equations, such as the average is computed as $\frac{1}{n} \sum_{i=1}^{n} x_{i}$. Or display equations like this:

$$
\begin{equation*}
|x|=
\begin{cases} x & \text{if $x\ge 0$,} \\
-x &\text{if $x\lt 0$.}
\end{cases}
\end{equation*}
$$

This is a Markdown document.

Medium header

It's easy to do italics or make things bold.

All models are wrong, but some are useful. An approximate answer to the right problem is worth a good deal more than an exact answer to an approximate problem.

Code block below. Just affects formatting here.

x <- 3 * 4

I can haz equations. Inline equations, such as the average is computed as $\frac{1}{n} \sum_{i=1}^{n} x_{i}$.

Or display equations like this:

\[ \begin{equation*} |x|= \begin{cases} x & \text{if $x\ge 0$,} \ -x & \text{if $x\lt 0$.} \end{cases} \end{equation*} \]

Markdown can be rendered to multiple formats

pandoc is a Swiss-army knife tool for conversion`

RMarkdown

RMarkdown is rendered to Markdown. The strength of RMarkdown, is that with an easy syntax, it is possible to mix ideas, code, and generated results seamlessly.

Input

This is an R Markdown document.

```{r sec_3}
x <- rnorm(1000)
head(x)
```

`knitr` offers a lot of control over representing different
types of output. We can also have inline `R` expressions
computed on the fly.

The mean $\bar{x} = \frac{1}{n} \sum_{i=1}^{n} x_{i}$ of the
`r length(x)` random variates we generated is
`r round(mean(x), 3)`.

This figure is computed on-the-fly as well. No more
copy-paste, including for figures:

```{r sec_4}
plot(density(x))
```

Output

Rendering can be automated is thus repeatable

From within R:

rmarkdown::render("filename.Rmd")

From the command line:

$ Rscript -e "rmarkdown::render('filename.Rmd')"

Summary

RMarkdown enables ideas and questions, the code that implements them, and the results generated by the implementation, to all stay together.
RMarkdown toolchain allows automated, repeatable rendering
- for publishing to the web and viewing through a browser
- and (through LaTeX) to obtain a submittable manuscript (in PDF or Word).
knitr is not limited to executing R code. See the book Dynamic documents with R and knitr by Yihui Xie, part of the CRC Press / Chapman & Hall R Series (2013). ISBN

Key Points

RMarkdown and knitr are powerful tools.

Output can be rendered in many formats.

You don’t need to know HTML!

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