Disclaimer This code is a modified version of Syntagmatic's Parallel Coordinates. Originally I just needed that code to work with D3 version 4 and saw that no plans to port the graph to version four were in the works. I must give credit where credit is due, and thank syntagmatic and all the other contributors for all the hard work they put into coding this complex and useful graph.
License MIT, do whatever you want with this! I just hope it helps people out!
Holding down the ctrl button will enable multi-brush mode. This will allow the user to put multiple brushes on a single axis.