What's the point of Column Definition in JSVIZ?
I'm trying to get through the JSVIZ tutoriol, and I have been having trouble with the material. It doesn't always explain why an analyst is using the methods that they are choosing to do. The one that confuses me is in the second JSVIZ tutorial labeled "JSViz Tutorial #2" using the Doughnut Table example for d3.js. I'm not too sure what the point in the Calculated Expression in the Column Definition is especially when it's being used in the JSVIZ. What's the point of Column Definition and Calucated Expressions?
It doesn't look like you are selecting the columns you want to use in Column Definition, but instead you're organizing the data by grouping it or using calculated expressions. If this is so then what's the point of using d3.js? D3.js is also grouping the data as well.
One example is what is First([Business Location]) doing in the tutorial? If you navigate to the Calculated Expression tab and insert First([Business Location]), and click on Preview you'll see that the output is different than the one in JSVIZ. The First() function literally just returns the First value of the column, but in the Dougnut example I'm really not sure what it is returning.