compute function of datatable

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C#

I want to use compute function of datable to get sum and avg of column group by to available columns in dataset and give result like query to bind this to an gridview.

e.g
I have result of query with 13 columns and I have to show these result according columns select by User from list.

of which if user have selected suppose following columns

empID varchar(200),
emp_Name varchar(200),
Performance numeric(8,2)

and now i have datatable of above mentioned columns

so here I have to calculate sum of Performance according to other columns in the table so how should i do it?
I need result again to assign datasoure to gridview

If you have other solution then please share.