Averaging Multidimensional Data for D3 Part 2

In my previous tutorial, I showed you conceptually how to average the data such that the 3 pieces of data in each row are averaged together and only 1 bar and text is shown per row for each average. This time I'm actually going to backtrack to the code I was using in the tutorial before that so that I can show you another way of averaging the data.

What we're going to average this time are not the 3 pieces of data per row (we're going to leave those alone this time); instead, we're going to average all of the elements each with a unique "Site Type" and "Media Type" value together.