Sorting by document order of some other element

it's been a couple of years since I've had need to consult with all
the wise guru's here, but I've got a question on a sorting problem
that I can't see a simple answer to at the moment.  Basically, I've
got two sets of elements, the element name is unknown but will match
in both sets.  I would like to walk the second set of elements (via a
for-each) and copy them in the order of the corresponding order of the
first set of identically named elements.  There will be an attribute
(say "id") that will have a one to one correspondence between both
sets of elements  .  Eg:

<doc>
 <set1>
     <element id="4"/>
     <element id="7"/>
     <element id="1"/>
     <element id="3"/>
     <element id="2"/>
 </set1>
 <set2>
     <element id="1">other stuff a</element>
     <element id="4">other stuff b</element>
     <element id="3">other stuff c</element>
     <element id="2">other stuff d</element>
     <element id="7">other stuff e</element>
 </set2>
</doc>

 <set2>
     <element id="4">other stuff b</element>
     <element id="7">other stuff e</element>
     <element id="1">other stuff a</element>
     <element id="3">other stuff c</element>
     <element id="2">other stuff d</element>
 </set2>

--
Peter Hunsberger