Thank you for writing.
We have a documentation article providing detailed information how custom aggregate functions can be created and used in RadPivotGrid
: Custom Aggregation
If you follow the suggested in the article approach you would be able to display the custom aggregate in the field list control associated with your pivot. Adding this function to the aggregate options dialog is, however, more tricky. That is why I have extended the example to include a solution handling this scenario. The default dialogs used in RadPivotGrid
can be substituted by creating a dialog factory: Customizing the Dialogs
I hope this helps. Should you have further questions please do not hesitate to write back.
Check out the Windows Forms project converter, which aids the conversion process from standard Windows Forms applications written in C# or VB to Telerik UI for WinForms. For more information check out this blog post
and share your thoughts.