how can i do this operation where i am adding two row values and placing them on the above row , which groups the below two rows … i want to display the added data when they are grouped and hide the data when they are un grouped .
Starting from Webix 2.1 you can use math cells with custom formulas.
In above case you can define a custom function, that will calculate necessary data for child rows, and set this math formula as value for the parent row.