PO mapping, Grouping target nodes and conditional subnodes

Hi experts (excuse my bad english)

we have a development to process information from our POS systems (this is a 10+ years old development, making by a java adapter module); now we need to migrate as a native PO development.

My "solution" to process the files, is:

1) make a generic structure with 1 header and multiple details node. ( done )

2) Grouping the source structure as :

common information (1 node)

- Nodes with a filter ( 0 ... unbounded )

some like this:

this is my generic initial structure:

i need create a structure grouping data by combination of Fecha, Terminal and Transaccion, like this:

For the first grouping level (target element DT_CommonValues ) is have the next mapping (and it works =) ):

but now, a have troubles to do the subtree (a copy of the original nodes, but filtering ...

do you have any idea??

thanks a lot in advanced.