Hi Leo,

I came across this question because I needed to know whether there are city

elements twice in the file. For that I wrote version 2 and the result was wrong. Then I wrote version 1 with … satisfies . => deep-equal($city) that gave the correct answer. I noticed that I do not fully understand the cast behavior of the = operator…

Thanks. deep-equal() is probably what you want. If you use generalized comparisons (=, !=, etc.), or if you use “data(.)” or “string(.)”, the descendant text nodes of the referenced node will be concatenated and returned as single string. As a result, queries like the following one…

<a><b>X</b></a> = <a><c>X</c></a>

…will return “true” because the atomized value of both operands is“X”.

Sibling node traversals are often slow, as the same nodes are repatedly processed.

for $city-group in //city group by $string := serialize($city-group) where count($city-group) > 1 return head($city-group)

With the latest BaseX 11 snapshot and the upcoming XQuery 4 features, it could be:

for value $v in map:build(//city, serialize#1) where count($v) > 1 return head($v)

Hope this helps, Christian