Hello Willem.

I apologize, but I'm not sure what you're trying to achieve.

If you enable row grouping for a column that has number values and you enable the "Calculate average" slider- the data wouldn't be displayed at all, since the column will be converted into a row.

On the other hand - if you enable row grouping for a column that has string values, you can enable the "Calculate average" slider for the other column that has number values, and it should display the AVG on the bottom.

Best regards.

OK, Willem.

That is default behavior of charts engine, but if you need some custom solution you can check in our documentation about wpDataCharts callbacks. 

• Every chart exposes several options that customize its look and feel. Charts usually support custom options appropriate to that visualization. wpdatachart callbacks  allows adding options that are available in Google Charts API, Highcharts API and Chart.js API. 

• All necessary resource are available in charts engines API (depends on which one you use). Every engine has different approach of charts settings. In wpdatachart callbacks you have to adopt those settings to wpdatachart object(you can take a look an example for each engine in our documentation and also in Support help center). Huge number of examples for any area of programming you can find on stackoverflow.com(typing your problem in google and of the end add site:stackoverflow.com and google will search only on that website) and also a lot of resource of examples of chart, chart settings and customization you can find on jsffidle. net(typing in google for example line chart highcharts jsffidle)
• Please note that using hooks or wpdatatable and wpdatachart callbacks requires certain level of programming skills and included support refers only to advises.

You can take a look at Highcharts dataGrouping and approximation and it may provide some insight into this.

Best regards.