Aggregating Data in Mongo Charts

Hi, I am having trouble getting some data into my table chart. I am trying to get a total count of each (grouped) row, and then to further do some work on that number (in my case, getting a percentage of completed users vs. total users). I can get the total users by adding a grouped ID fields and adding it to the mongo table under ‘values’, and using the sum option. I am trying to get that number to use against completed count, which is an existing field in the table. Is there a way to do this?