Introduction to the Unix Command Line

####Homebrew

Brew is a fantastic package manager for Mac that will allow you to easily install packages.
http://mxcl.github.io/homebrew/

###Install Brew

ruby -e "$(curl -fsSL https://raw.github.com/mxcl/homebrew/go)"

####GitHub

brew install git

Note: If you have issues with the brew install because of an XCode error, try using this Heroku Toolbelt installation that will include git, or choose an OS based installation from this guide: http://git-scm.com/book/en/Getting-Started-Installing-Git On Windows, there's an installer available here: http://git-scm.com/download/win

###Getting the 538 Data

git clone https://github.com/jseabold/538model

Processing the data

First, we may want to get some general id of what is in the folder. Here we will use to two basic command, cd, to change directory and ls to list the files

cd 538model/data
ls

Next we want examine the data and perhaps how much data we have in the census file. We'll use less to get a preview of the files or cat to print the whole file. wc gets a word count of the file and wc -l gets a line count.

less census_demographics.csv
cat census_demographics.csv
wc census_demographics.csv
wc -l census_demographics.csv

This file is comma-separated, so we can use the cut command to view individual columns.

cat census_demographics.csv | cut -d',' -f1,3

Now, we can also get some basic information on the top educated states. College-level education rate is the 6th column and sort let's us order the results

cat census_demographics.csv  | cut -d',' -f1,6 | sort -t',' -nr -k2

Looking at the poll data, we may want to do some basic aggregation. Let's find out what states had the most polls. The 8th field has the state. uniq -c gives us a count of each unique element. Note, sort must always proceed uniq as it expects sorted input.

cat 2012_poll_data_states.csv  | cut -f8 | sort | uniq -c | sort -nrk2

Our results look a bit funny - we've got "State" mixed in since it was a header column. We can skip that row by using tail which gives the last n lines. tail +n gives all but first n lines.

cat 2012_poll_data_states.csv  | cut -f8 | tail +n2 | sort | uniq -c | sort -nrk2

We may want to look at just the September polls, since those were the latest polls in the files. How many polls were in September. We can filter using grep, a command that let's us search for a string in each line.

cat 2012_poll_data_states.csv | grep ^9 | wc -l

We can also use grep to find out how many polls had Obama leading and how many had Romney ahead.

cat 2012_poll_data_states.csv | grep ^9 | grep "Obama +" | wc -l
cat 2012_poll_data_states.csv | grep ^9 | grep "Romney +" | wc -l

Funny enough, this doesn't match the total number of polls in September. Let's use grep -v which returns all lines without the search string to see what the other rows are.

cat 2012_poll_data_states.csv | grep ^9 | grep -v "Obama +" | grep -v "Romney +"

These polls returned are all ties with neither candidate ahead.

###In Class Examples

• How can we extract all polls that were in Ohio?
• How can we find out which polling company polled most often?

Other data processing tools available on Unix

• awk
• sed
• perl