XQuery / BaseX - Limit depth of result

Question

When using XPath or XQuery, is there a way to limit the depth of the result?

I am using BaseX, which supports XQuery 3.1 and XSLT 2.0.

For example, given this input document:

<country name="United States">
  <state name="California">
    <county name="Alameda" >
      <city name="Alameda" />
      <city name="Oakland" />
      <city name="Piedmont" />
    </county>
    <county name="Los Angeles">
      <city name="Los Angeles" />
      <city name="Malibu" />
      <city name="Burbank" />
    </county>
    <county name="Marin">
      <city name="Fairfax" />
      <city name="Larkspur" />
      <city name="Ross" />
    </county>
    <county name="Sacramento">
      <city name="Folsom" />
      <city name="Elk Grove" />
      <city name="Sacramento" />
    </county>
  </state>
</country>

If I execute this query: /country/state, I get the following result:

<state name="California">
  <county name="Alameda">
    <city name="Alameda"/>
    <city name="Oakland"/>
    <city name="Piedmont"/>
  </county>
  <county name="Los Angeles">
    <city name="Los Angeles"/>
    <city name="Malibu"/>
    <city name="Burbank"/>
  </county>
  <county name="Marin">
    <city name="Fairfax"/>
    <city name="Larkspur"/>
    <city name="Ross"/>
  </county>
  <county name="Sacramento">
    <city name="Folsom"/>
    <city name="Elk Grove"/>
    <city name="Sacramento"/>
  </county>
</state>

I would like to limit the depth of the result. Ideally, there'd be a way for me to specify the depth, rather than hard-coding an XPath query.

As an example, I would like to limit the result to the result nodes and its children, but not including the grandchildren, so the result would be:

<state name="California">
  <county name="Alameda" />
  <county name="Los Angeles" />
  <county name="Marin" />
  <county name="Sacramento" />
</state>

Answer 1

One easy and straightforward way is to use XSLT-2.0 with an empty template cancelling all children of <county>. The <xsl:strip-space> removes the space that would have been used by the children.

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
  <xsl:strip-space elements="*" />
 
  <!-- Identity template -->
  <xsl:template match="@* | node()">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()" />
    </xsl:copy>
  </xsl:template>
  
  <xsl:template match="/">
      <xsl:apply-templates select="/country/state" />
  </xsl:template>
  
  <xsl:template match="county/*" />
  
</xsl:stylesheet>

Output is:

<?xml version="1.0" encoding="UTF-8"?>
<state name="California">
    <county name="Alameda"/>
    <county name="Los Angeles"/>
    <county name="Marin"/>
    <county name="Sacramento"/>
</state>

---

With XQuery, a solution could look like this:

for $st in doc("b.xml")/country/state return
  element { node-name($st) } { $st/@*,
  for $ct in $st/county return 
    element { node-name($ct) } { $ct/@* }
  }

The output is the same.