UDF to generate childs by source key

Hi gurus,

I need help with an UDF. I'm trying to create a target structure, i have been able to create the child nodes needed but i have problems generating the <data_grouped> segment. Let me show the structures :

Source structure

<root>

     <child>
          <key1>
          <key2>
          <key3>
          <data1>
          <data2>
          <data3>
     </child>

     <child>
          <key1>
          <key2>
          <key3>
          <data4>
          <data5>
          <data6>
     </child>

     <child>
          <key4>
          <key5>
          <key6>
          <data7>
          <data8>
          <data9>
     </child>

</root>

Target structure:

<root>

     <child>
          <key1>
          <key2>
          <key3>
          <data_grouped>
               <data1>
               <data2>
               <data3>
               <data4>
               <data5>
               <data6>
          </data_grouped>
     </child>

     <child>
          <key4>
          <key5>
          <key6>
          <data_grouped>
               <data7>
               <data8>
               <data9>
          </data_grouped>
</child>

</root>

if same key1/key2/key3 then append data to target gruped by key1/key2/key3

Could you give me some light please??

Kind regards