This file can be used (in conjunction with the appropriate JavaScript libraries noted in the code) with a copy of the csv of book sales from Leanpub. It is a file designed to be available in conjunction with the blog post on d3noob.org that investigated changes in book downloads.
The csv file should have a search and replace carried out on it to replace all instances of a white space (an ordinary ‘space’ character) with an underscore ‘_’.