HW#4 - First cut at D3 plot for final project

Homework 4
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Author: Ryan Quan (rcquan)  
Date: 2014-11-20  
GitHub: [www.github.com/fryandata/ecstasy](www.github.com/fryandata/ecstasy)

## Description

This D3 plot is intended to answer the following question:

**Out of all pills sold as ecstasy for a given year, how often was chemical X present?**

With the owner's permission, we used R's `XML` package to scrape XML data from [EcstasyData.org](www.ecstasydata.org). We then used `dplyr` for data cleaning and wrote the resulting data to JSON using `RJSONIO`.

## TODO

1. Fix the axis so that movement of points is more apparent.
2. Remove labels for clump of points below y = 0.05. 
3. Add tooltips for more information about chemical compound on hover.
4. Add path transitions to make rank changes more apparent between years.
5. Color points by activity type: "dissociative", "stimulant", etc.
6. Add zoom feature.
7. Add option to remove "MDMA" from graph.