Compare attributes from different levels during xslt transformation - xslt

Question

Below I created a simplyfied XML example of what my xml looks like. I have an attribute which contains a number that I would like to watch. It's sort of a counter and during the transformation I would like to add something whenever the counter ++.
The problem is the number of levels in my xml file. Here I only made three but I actually have like 8 or maybe even more. I need to find a way to compare the current node against the previous one (or vice versa) but with the levels taken into account. So for instance in the example below the lvl2 node with the id of 4 needs to be compared with the lvl3 node with id 3 simply to find out if the id attribute has been raised.
xml:
<lvl1 id="1">
<lvl2 id="1">
<lvl3 id="1"></lvl3>
<lvl3 id ="2"></lvl3>
</lvl2>
<lvl2 id="2">
<lvl3 id="3"></lvl3>
</lvl2>
<lvl2 id="4"></lvl2>
</lvl1>
Since global counter variables are out of the question with xslt Im currently out of ideas and can't seem to find any here or anywhere else..
the output would be something like:
<ul>
<div>id 1</div>
<li>
<ul>
<li>
<ul>
<li></li>
<div>id 2</div>
<li></li>
</ul>
</li>
<li>
<ul>
<div>id 3</div>
<li></li>
</ul>
</li>
<div>id 4</div>
<li></li>
</ul>
</li>
here the stylesheet which transforms the xml into the html output but without the divs:
<?xml version="1.0" encoding="UTF-8"?><xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/">
<ul>
<xsl:value-of select="#id"/>
<xsl:apply-templates select="lvl1"/>
</ul>
</xsl:template>
<xsl:template match="lvl1">
<li class="{#id}">
lvl 1
<ul>
<xsl:apply-templates select="lvl2"/>
</ul>
</li>
</xsl:template>
<xsl:template match="lvl2">
<li class="{#id}">lvl 2
<ul>
<xsl:apply-templates select="lvl3"/>
</ul>
</li>
</xsl:template>
<xsl:template match="lvl3">
<li class="{#id}">lvl 3
</li>
</xsl:template>

Answer 1

If you apply this XSLT
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html" />
<xsl:template match='/'>
<ul>
<xsl:apply-templates select='*' />
</ul>
</xsl:template>
<xsl:template match="*">
<li>
<div>
<xsl:value-of select='#id' />
<xsl:if test='count(*)>0'>
<ul>
<xsl:apply-templates select='*' />
</ul>
</xsl:if>
</div>
</li>
</xsl:template>
</xsl:stylesheet>
you get something that may be what you ask:
<ul>
<li>
<div>1<ul>
<li>
<div>1<ul>
<li>
<div>1</div>
</li>
<li>
<div>2</div>
</li>
</ul>
</div>
</li>
<li>
<div>2<ul>
<li>
<div>3</div>
</li>
</ul>
</div>
</li>
<li>
<div>4</div>
</li>
</ul>
</div>
</li>
</ul>

Answer 2

The question is a bit more complex than it seems, as preceding:: does not always work here to find last #id before current element. You need also check #id on parent and consider root position as well. This code produces the desired result with the XML given in the question. See my comments inside.
<xsl:template match="/">
<ul>
<xsl:apply-templates/>
</ul>
</xsl:template>
<xsl:template match="*">
<!-- get preceding (or parent) id -->
<xsl:variable name="lastId">
<xsl:choose>
<!-- try to get id from first preceding element -->
<xsl:when test="preceding::*[1]/#id">
<xsl:value-of select="preceding::*[1]/#id"/>
</xsl:when>
<!-- there could still be ids in parent elements -->
<xsl:when test="../#id">
<xsl:value-of select="../#id"/>
</xsl:when>
<!-- or this is the root element -->
<xsl:otherwise>
<xsl:value-of select="0"/>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>
<!-- now compare current and last id -->
<xsl:if test="#id > $lastId">
<div>
<xsl:text>id </xsl:text>
<xsl:value-of select="#id"/>
</div>
</xsl:if>
<!-- create list item -->
<li>
<!-- check for subelements -->
<xsl:if test="*">
<ul>
<xsl:apply-templates/>
</ul>
</xsl:if>
</li>
</xsl:template>
Depending on your real scenario, you might want to limit match="*" to match="*[starts-with(local-name(),'lvl')]", as proposed in a comment by LarsH.