Aggregation of XML elements (sum, grouping and unique values) - xquery

Question

I am new in xquery. Can you please suggest xquery to get the below output xml.
Input xml :
<elem count="4" name="ABC">
<elem count="3" name="VAl_1">
<elem count="1" name="VAl_2">
</elem>
<elem count="5" name="PQR">
<elem count="2" name="VAl_1">
<elem count="3" name="Val_3">
</elem>
Output xml:
<elem count="9" name="ABC,PQR">
<elem count="5" name="VAl_1">
<elem count="1" name="VAl_2">
<elem count="3" name="VAl_3">
</elem>
I have parent node with count and name as attr. When I combine the parent node. count values should get added for parent as well as for children if they having same name.
This should be done in recursive way for any no of parents.

Answer 1

I made a few assumptions, but the following solves at least the problem as stated:
declare variable $input :=
<input>
<elem count="4" name="ABC">
<elem count="3" name="VAl_1"/>
<elem count="1" name="VAl_2"/>
</elem>
<elem count="5" name="PQR">
<elem count="2" name="VAl_1"/>
<elem count="3" name="Val_3"/>
</elem>
</input>/*;
<elem count="{ sum($input/#count) }"
name="{ string-join(distinct-values($input/#name), ',') }">
{
for $name in distinct-values($input/elem/#name)
let $grp := $input/elem[#name eq $name]
return
<elem count="{ sum($grp/#count) }" name="{ $name }"/>
}
</elem>
The first half of the code is just declaring a variable with the example input. The query itself is an element template using simple sum() and distinct-values() call to provision both attributes.
The interesting part is the for loop. By looping over distinct values for #name, then for each of them selecting all elem with the same value, it actually makes a grouping of the elems using the key #name.