QPM Lab 2: Data Visualization & Descriptive Statistics in R and R Commander

QPM Lab 2:

Data Visualization & Descriptive Statistics

in

R

and

R

Commander

Viktoryia Schnose & Betul Demirkaya

Department of Political Science

Washington University, St. Louis

September 4, 2013

A Reminder From Last Class

1

Open

R

2

Write the following in the command line:

library(Rcmdr)

3

This way, you open the package from the

R

library. It does

not

open

automatically.

4

A new

window

should have opened. This is

R commander

.

5

Go to the website for QPM.

6

Open the Class Datasets.

Goals for the Class

•

Reading a dataset & viewing the dataset with

R commander

•

Re-coding a variable to a factor

•

Descriptive Statistics with

R commander

•

Bar graphs with

R commander

Reading Data with

R

: Answering Two Questions

1

What type of file do you have?

•

.csv

= comma separated values

•

.txt

= text file

•

.dta

= STATA file

•

.spss

= SPSS file

2

Where is the file?

•

Saved in your computer

•

Online in a url

Reading Data with

R

:

.csv

or

.txt

STEP 1: What type of file are we using for the homework?

Reading Data with

R

:

.csv

or

.txt

STEP 2: Where is the file for the dataset for this week’s HW?

See Appendix for how to enter the URL.

Brazil Dataset: Viewing the Dataset

Active

Dataset

Variable

name

Observation

number

Click here

Brazil Dataset: Converting

vote

variable into

a factor = qualitative variable

Brazil Dataset: Converting

vote

variable into

a factor = qualitative variable II

Select

vote

variable.

Brazil Dataset: Converting

vote

variable into

a factor = qualitative variable III

Specify what each numeric value means (read the codebook).

Wednesday, September 7, 2011

Brazil Dataset: Frequency Distribution for

vote

variable

Statistics

→

Summaries

→

Frequency distributions

Brazil Dataset: Bar Graph for

vote

variable (frequency)

Graphs

→

Bar Graph

→

vote

no yes vote F re qu en cy 0 200 400 600 800

See Appendix for another way of presenting the same data.

In class assignment

•

Break into groups of 3 or 4 individuals

•

Fill out the sheet. ASK QUESTIONS.

•

If you finish early, try to draw a bar graph for

vote

variable that

shows probabilities. See Appendix for help.

Appendix: Table of Contents

•

Using

R

&

R Commander

•

Reading

.csv

or

.txt

files from the internet

•

Frequency distribution: Difference between

R

script and

R

output

•

Another graph for vote variable showing probability

•

R

code to obtain the bar graph with probability

Using

R

&

R Commander

Drop down

menus

Toolbar

Script Window

:

Here you will see R commands

generated by the GUI.

You can write commands here.

Select them by highlighting them and press ‘Submit’

Output Window

:

Dark Blue

: printed output

Red

: command used

Message Window:

Red

- Error Message

Green

- Warning

Dark Blue

- Other

information

Reading Data with

R

:

.csv

or

.txt

From the Internet

STEP 3: Writing down the

URL

for the Brazil dataset.

Prof. Montgomery’s website

Difference between R Script and R Output

Output

Script

Wednesday, September 7, 2011

Brazil Dataset: Bar graph for

vote

variable (probability)

no yes

Did you vote in the last presidential election?

Pro ba bi lit y 0 20 40 60 80

Brazil Dataset: Bar graph for

vote

variable (probability)

This is how to modify the code to obtain the previous plot.

barplot(table(brasil$vote)*100/sum(table(brasil$vote)),

xlab = "vote", ylab="Probability")