# Introduction

This is an introductory post into using Bookdown. Bookdown is a powerful package that allows you to create documents embedding images, tables, and code. One great reason to use Bookdown is that you can put results and images from your code directly into your text, which reduces the chances of copying errors. For this post, I’m going to focus on creating an HTML document, though you can also create outputs in Word and PDF formats. To create PDFs, you will also need to download LaTeX. Note: throughout this document, I will be showing a code in separate boxes. To get the code to display, instead of run, the code will be commented out (with “#”). To actually run the code, you will need to remove the comment character.

# Formatting text

The first part of this will discuss different text formatting. This is not an extensive list of what you can do with R Markdown and text, but it will cover the basics. The top part of the document is the YAML, which stands for Yet Another Markup Language. The YAML has a lot of the commands which control the formatting of your text. For this presentation, we’re going to keep it simple, and only include the basics. The YAML goes at the top of the document. Some items are optional, such as the title, author, and date, but output format is necessary.

YAML:

---
title: "This is my title"
author: "Name here"
date: "Today's date"
output:
bookdown::html_document2
---

## Italics

Markdown:

*words*

Output:

words

## Bold

Markdown:

**words**

Output:

words

## Bullets

Markdown:

* words
* more words

Output:

• Words
• More words

Markdown:

# Top level header
## Second level header
### Third level header
#### Fourth level header

Note: in Bookdown, you can add {-} if you don't want the header to be numbered. 

Output:

# Top level header

## Second level header

### Third level header

#### Fourth level header

You can add code by putting in three backticks:

# 
# Code goes here
# 

You can choose different languages by defining the languages in the curly brackets

# {r}
# Code in R
# 
# {python}
# Code in python
# 

## Muting code

Sometimes, you want to run the code without displaying it or the output. In the curly brackets, you can add in information on how you want the code to perform.

# {r include = FALSE}
# print("Include determines whether the code and output is put into the text or not")
# 

## Showing output without code

Other times, you may want to show the output, but without showing the code. The “echo” commands controls whether the code displays or not.

# {r echo = FALSE}
# print("The echo command removes the code")
# 
## [1] "The echo command removes the code"

## Showing code without output

If you want to display the code without running it, you can use the “eval” command.

# {r eval = FALSE}
# print("The eval command determines whether you run the code.")
# 
print("The eval command determines whether you run the code.")

## Removing warnings and error messages

Often, you can get warnings and messages which you don’t want to display in your documents, especially when loading packages. You can control whether these display with the “message” and “warning” commands.

# {r message = FALSE, warning = FALSE}
# pint("Message controls whether messages display.")
# print("Warning controls whether warnings display.")
# 
## [1] "Message controls whether messages display."
## [1] "Warning controls whether warnings display."

## Inline code

You can also show the code inline.

Two plus two = #r 2+2

Two plus two = 4

## From a disk

To add an image from a disk, you have to point the code to where you want it to look

# {r}
#knitr::include_graphics('folder/file.jpg')
#

## From your code

But you can also add in images from your code. This is one of the most useful functions of R Markdown because any time you update the code, it will automatically update the image.

# {r}
# plot(mtcars$hp, mtcars$mpg)
# 

## Referencing figures

You can also caption figures and refer back to them in the text.

Plot the image in the code:

# {r hp, fig.cap= "Relationship between horsepower and miles per gallon"}
# plot(mtcars$hp, mtcars$mpg)
# 

Then call the image in the text (Figure \@ref(fig:hp)).

Then call the image in the text (Figure 1).

You can do the same for figures you call from your disk:

# {r horseshoe, fig.cap = "Horseshoe Bend"}
#knitr::include_graphics('folder/file.jpg')
#
#Look at this picture of Horseshoe Bend (Figure \ref@(fig:horseshoe)).
#

Look at this picture of Horseshoe Bend (Figure 2).

R-markdown is not great for tables. However, there is the kable function in Knitr, which is really useful.

#{r foo}
#install.packages("knitr")
#library(knitr)

#knitr::kable(
#  caption = "The first few rows of mtcars"
#)
#
#Check out some data in Table \@ref(tab:foo)
#
Table 1: The first few rows of mtcars
mpg cyl disp hp
Mazda RX4 21.0 6 160 110
Mazda RX4 Wag 21.0 6 160 110
Datsun 710 22.8 4 108 93
Hornet 4 Drive 21.4 6 258 110
Hornet Sportabout 18.7 8 360 175
Valiant 18.1 6 225 105

Check out some data in Table 1

Inline equations are denoted with the $This is my equation:$\alpha = \beta$ This is my equation: $$\alpha = \beta$$ ## On a separate line If you want your equation to appear on a separate line, you can use $$This is my equation:$$ \alpha = \beta$\$

This is my equation: $\alpha = \beta$

## Referenced equations

Often, you want to number your equations so you can refer to them in the text. This takes a little bit more work but is still do-able.

$$\alpha = \beta (\#eq:alpha)$$

This is a numbered equation:

$$$\alpha = \beta \tag{1}$$$

Refer to Equation (1).