This is a tutorial for R markdown. It also serves as a sample R markdown code. Please check the source code of this document.

- Think of it as a source code for creating a webpage that can embed R code
- You write a source code and “compile” it to create a webpage

In RStudio, click **File -> New File -> R
Markdown…**.

RStudio will create a skeleton file with some basic explanations. Read those.

You can compile the source code into HTML or PDF. I recommend HTML because it can adjust fontsize, linebreak, etc. according to the device.

First of all, check the R markdown cheatsheet: https://www.rstudio.com/wp-content/uploads/2015/02/rmarkdown-cheatsheet.pdf

Especially, check

**3. Markdown**.It covers most of what you need to know to write plain text

If you know LaTeX, a popular language for writing academic documents, you can use it in R markdown.

R markdown understands LaTeX syntax — just write them.

For the class, we use it to write math symbols and equations, which we discuss below.

Please check the source code of this document to see how to write math equations.

Pythagorean theorem.

\[ a^2 + b^2 = c^2 \]

Arithmetic mean \(\geq\) Geometric mean \(\geq\) Harmonic mean.

\[ \frac{1}{n}\sum_{i=1}^N X_i \geq \left( \prod_{i=1}^N X_i \right)^{1/N} \geq \frac{1}{\sum_{i=1}^N 1/X_i}. \]

Greek letters, plain texts and multiple lines.

\[ \begin{aligned} line 1 &= \alpha + \beta \\ \text{plain text} &= \gamma + \delta \\ line 3 &= \lambda + \sigma \\ \textbf{bold plain text} &= \Lambda + \Sigma \end{aligned} \]

Caligraphic, blackboard bold and bold. \[ \mathcal{F}, \mathbb{F}, \mathbf{F}. \]

If you need a math symbol but you don’t know what to type, go to http://detexify.kirelabs.org/classify.html and draw the symbol using your mouse! For example, you can draw \(\pm\) there and see that the command is “pm”.

The main advantage of using R markdown is that we can run R within the document.

In other words, we can alternate between plain text and R code.

In terms of homework submission, this is handy because you don’t need to separately submit the code or copy the R output into the document.

Below is an example of the R code (which we shall call “chunk”) run within the document.

```
Sys.setenv(lang="EN") ### this command sets the R locale to English ###
courseNo = "ECON 21130"
print(courseNo)
```

`## [1] "ECON 21130"`

Note that it displays not only the code but also the result.

Also, the R chunks are cumulative; that is, the variable

`courseNo`

defined in the above can be used in the later chunks.

Below is an example.

```
courseTitle = "Topics in Microeconometrics"
print(paste(courseNo, courseTitle, sep = " - "))
```

`## [1] "ECON 21130 - Topics in Microeconometrics"`

R markdown offers options to configure how the R chunks are displayed. For example, you can decide whether to hide the code, whether to hide the result, whether to display the error message, etc.

For a list of such options, check

**5. Embed code**of the R markdown cheatsheet.For example,

`eval=FALSE`

option tells R to not execute the code.

Below is an example.

`ROOT2 = 1.414`

In the above chunk, I specified `eval=FALSE`

option. So
the above chunk is not executed, which means `ROOT2`

is not
defined.

In the below chunk, we can confirm that `ROOT2`

is not
defined.

`print(ROOT2)`

`## Error in print(ROOT2): object 'ROOT2' not found`

If you check the source code of this document, you will notice that I
specified `error=TRUE`

in the above chunk.

You must specify this option if you want R to print the error message. Otherwise the source code will not be compiled into the HTML document due to the error.