Week 02 - More Introduction to R

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# Week 02 - More Introduction to R
## Writing Scripts and Reading Data Files
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### Danilo Freire
### 28th January 2019

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# Today's Agenda

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* Course website

* Brief recap

* Questions about `swirl()`

* Create and run R scripts

* Read `.csv` datasets

* Homework: install RMarkdown and write your first document
]
---

# Course website

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* The course website has a new address:

* <http://pols1600.github.io>

* Syllabus, lecture slides, R scripts, assignments, datasets

* Updated syllabus at <https://cab.brown.edu/>

* [danilo_freire@brown.edu](mailto:danilo_freire@brown.edu)

]

---

# Brief recap

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* Last week you learned how to:

- Install R and RStudio
    
  - Do arithmetic operations in R

- Manipulate vectors

- Install packages from CRAN

- Use `swirl()`
  
  - Do the course exercises
]
---

# Brief recap

```r
(2^5)*3.5
```

```
## [1] 112
```

```r
vec <- seq(from = 1, to = 100, by = 2)
vec[c(5:10)]
```

```
## [1]  9 11 13 15 17 19
```

```r
summary(vec)
```

```
##    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
##     1.0    25.5    50.0    50.0    74.5    99.0
```

```r
install.packages("congressbr")
```

```
## 
## The downloaded binary packages are in
## 	/var/folders/nl/c_4v70mj40g0y7p_9vb6r68r0000gq/T//RtmpV1L5k9/downloaded_packages
```

```r
library("swirl")
```

```r
swirl()
# R won't read this line
```
---

# Swirl

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* Questions?
]
---

# R scripts

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* Why should we write scripts?

- Save time: automate boring tasks

- Reproducibility

- Allow complex tasks to be performed in small steps

- Faster to run
]
---

# R scripts

.center[![:scale 110%](script.png)]
---

# Read data files

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* R can read files of many types and formats

* Usually, data are either in `.csv` or `.Rdata` format

* R can also read Excel spreadsheets with the [readxl package](https://readxl.tidyverse.org/)

]
---

# Read csv files

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name_object <- read.csv("data_path/file.csv")
]
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---
# Read csv files

```r
*df <- read.csv("/Users/politicaltheory/Documents/github/pols1600.github.io/datasets/turnout.csv")
summary(df)
```

```
##       year           VEP              VAP             total       
##  Min.   :1980   Min.   :159635   Min.   :164445   Min.   : 64991  
##  1st Qu.:1986   1st Qu.:171192   1st Qu.:178930   1st Qu.: 73179  
##  Median :1993   Median :181140   Median :193018   Median : 89055  
##  Mean   :1993   Mean   :182640   Mean   :194226   Mean   : 89778  
##  3rd Qu.:2000   3rd Qu.:193353   3rd Qu.:209296   3rd Qu.:102370  
##  Max.   :2008   Max.   :213314   Max.   :230872   Max.   :131304  
##                                                                   
##       ANES           felons         noncit         overseas   
##  Min.   :47.00   Min.   : 802   Min.   : 5756   Min.   :1803  
##  1st Qu.:57.00   1st Qu.:1424   1st Qu.: 8592   1st Qu.:2236  
##  Median :70.50   Median :2312   Median :11972   Median :2458  
##  Mean   :65.79   Mean   :2177   Mean   :12229   Mean   :2746  
##  3rd Qu.:73.75   3rd Qu.:3042   3rd Qu.:15910   3rd Qu.:2937  
##  Max.   :78.00   Max.   :3168   Max.   :19392   Max.   :4972  
##                                                               
##     osvoters  
##  Min.   :263  
##  1st Qu.:263  
##  Median :263  
##  Mean   :263  
##  3rd Qu.:263  
##  Max.   :263  
##  NA's   :13
```
---

# Read csv files from the internet

```r
*df <- read.csv("https://raw.githubusercontent.com/pols1600/pols1600.github.io/master/datasets/turnout.csv")
summary(df)
```

---

# Read csv files from the internet

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* In this course, you will be able to download all datasets directly from our website

* Just go to <http://pols1600.github.io/datasets>, click with the left buttom over the name of the dataset, then copy the code to your R script

]
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# RMarkdown

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* We can use R to write documents and websites, too

* RMarkdown is a very simple language to learn and use

* You should submit your assignments and final project in RMarkdown format

* Visit <https://rmarkdown.rstudio.com/lesson-1.html> for an introduction
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# RMarkdown

.center[![:scale 110%](rmd.png)]
---

# RMarkdown basics

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Add `fontsize: 12pt` to the header (the section above `---`)

Basic commands:

`# Section`

`## Subsection`

Formatting: `*italics*` `**boldface**`

Weblink: `[POLS1600 website](http://pols1600.github.io)`

Image: `![](path/to/picture.jpg)`

]
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# RMarkdown

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Lists: 
]

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You need to add four spaces or one tab to write sub-items
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---

# RMarkdown

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R code:

` ```{r}`

`library(swirl)`

` ``` `

Just click on the `insert` buttom to add code
]

.center[![:scale 100%](insert.png)]

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Then press the `knit` buttom to see your document
]
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# Homework

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* Install LaTeX: <https://www.latex-project.org/get/> (it is a _big_ file, ~2Gb)

* Download this pdf: <https://www.rstudio.com/wp-content/uploads/2015/02/rmarkdown-cheatsheet.pdf>

* Create a new RMarkdown document

* If RStudio asks you to download some packages, click `yes`

* Write a few paragraphs and add this code to the file:
]

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a <- seq(1:10)

b <- a*a

plot(a, b)
]

---

# Homework

.center[![:scale 85%](plot.png)]
---

# Homework

.center[![:scale 65%](doc.png)]
---

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# See you on Wednesday!