Bind dataset to datagrid with combobox column

I have a datatable with distinct rows like:

col1,col2,col3,col4
A,B,C,E
A,B,C,F
L,M,N,O
P,Q,R,S
P,Q,R,T
P,Q,R,U

Now, I want to bind the above to a datagrid containing 4 columns, with the 4th column being a combobox such that:
the first 3 columns are group by value and the 4th combobox column has the distinct values for this group

datagrid (combobox column items are shown in paranthesis here):
A,B,C,(E,F)
L,M,N,(O)
P,Q,R,(S,T,U)

How can I achieve the above?
Thanks

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sri