Matching only one of many unknown nodes with xpath

Question

Hello.

Im trying to match only one of each node with a generic match. Can this be done generic at all? I would have prefered to just match one of each node with the same local-name()

<xsl:variable name="xmltree">
  <node />
  <anothernode />
  <node />
  <anothernode />
  <unknown />
  <anothernode />
  <node />
  <unknown />
</xsl:variable>

<xsl:template match="/">
  <xsl:apply-templates select="$xmltree/*" mode="MODULE"/>
</xsl:template>

<xsl:template match="*" mode="MODULE" /> <!-- EMPTY MATCH -->

<xsl:template match="node[1]|anothernode[1]|unknown[1]" mode="MODULE">
  <!-- Do something -->
</xsl:template>

Answer 1

This is a grouping question and in XSLT 1.0 the most efficient way to do grouping is the Muenchian method.

If the number of elements is not too-big, the following short code might be sufficient:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"&gt;

 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

    <xsl:template match="/*/*">
     <xsl:copy-of select=
      "self::*[not(preceding-sibling::*
                      [name() = name(current())]
                   )
               ]"/>
    </xsl:template>
</xsl:stylesheet>

When this transformation is applied on the following source XML document:

<t>
    <node />
    <anothernode />
    <node />
    <anothernode />
    <unknown />
    <anothernode />
    <node />
    <unknown />
</t>

The wanted result is produced:

<node/>
<anothernode/>
<unknown/>

One may study the XPath expressions used in order to understand that this transformation copies really every first occurence of an element with a specific name.