How do I efficiently summarize my data for a ChartJS Doughnut or Pie?

I want to build a doughnut / pie / single series chart using ChartJS. This requires me to:

1. Fill in the total value into the Chart object

2. Fill in one value for each slice in the Dataset object

It's #2 that I'd like to know about: What is the easy way to get a total value for each of my slices to put into the Dataset? Outside of Mendix I'd do a Count/Group By query. What's the best practice within Mendix? How do I implement this in a Microflow?