unicity different rows

Hi there,


I have a structure on which I want to make a unicity sort. I don't know how 
to begin.
here it is what I have :

<1>
        <a/>
        <b/>
</1>
<2>
        <a/>
</2>
<3>
        <b/>
        <c/>
</3>
<1>
        <a/>
        <c/>
</1>

etc ...

And I want to sort the "number" by "letters" :
Here is what I want :

<1>
        <a/>
        <b/>
        <c/>
</1>
<2>
        <a/>
</2>
<3>
        <b/>
        <c/>
</3>


Thanks.
Lionel


Lionel CRINE
Ingénieur Systèmes documentaires
Société : 4DConcept
22 rue Etienne de Jouy 78353 JOUY EN JOSAS
Tel : 01.34.58.70.70 Fax : 01.39.58.70.70