Hi,
Get the ith value using the following expression.
count(../preceding-sibling::my:group2) + 1
get the xpath of the value which you want to display in the drop down (i.e., secondary data source xpath). Place the above expression in the index of repeating group.
For ex: xdXDocument:GetDOM("emp")/Emps/Emp[count(current()/../preceding-sibling::my:group2) + 1]/EmpID
Here emp is a secondary xml.