Filter between two dropdowndata windows

Hi,
I have a window that contains two dropdown datawindows calling from two procedures. I'm using PowerBuilder9

1.Function Desired: function     ( display value  : function_desc, data value : function)     fun1,fun2,fun3,fun4
2.corrected Code  : code_value ( display value : code_desc,      data value : code_value) cod1,cod2,cod3,cod4,cod5 and cod6

I need to filter in the second datawindow according to the first ddw selection.

If the user selects fun1 in drowdown(function desired) then I need to filter the 2nd ddw and shows only cod5,cod2 and cod6.
                           fun2 in drowdown(function desired) then I need to filter the 2nd ddw and shows only cod2.
                            fun3 in drowdown(function desired) then I need to filter the 2nd ddw and shows only cod1
                            fun4 in drowdown(function desired) then I need to filter the 2nd ddw and shows only cod1,cod2 ,cod3 and cod4.
I wrote the code in retreive event( window level) and itemchanged event ( dw level). But I am not able to do filter properly according to their selection.

I appreciate your help.