How to group data from xml

[umen]

How to group data from xml ?

Hello all

i dont understand somthing very fandamental in Ireport and its driving me crazy

i have simple xml data source

 

now in my report i like to order the nodes one after the other

and ater this the nodes .

but when i try place the nodes in the designer fields like this

$F{a1}

$F{b1}

what im getting in the privew is mix of both fields like this :

 

and i expect to get

what im doing wrong here ?