DataTable has same data but quantity column values are different, Sum the quantity column and make into single row

we can doit with a group by and sum up the group members

Assign activity:
LHS: dtResult | dataType: DataTable
RHS: YourOriginDataTableVar.Clone

Assign Activity:
LHS: dtResult

(From d in YourOriginDataTableVar.AsEnumerable
Group d by k1=d("PartNum").toString.Trim, k2=d("MaterialNum").toString.Trim into grp=Group
Let s = grp.Sum(Function (x) CInt(x("Req Qu").toString.Trim))
Let ra = new Object(){k1,k2,grp.First()("Vendor"),s}
Select r=dtResult.Rows.Add(ra)).CopyToDataTable

Also have a look here: