Bob Faist’s Blog

The idea here is that if a <para> is preceded by 1 or more notes, they need to be grouped with the <para> in a <group> node.  The problem is how do you write the Xpath to only grab the <note> nodes which are between the current <para> and the previous <para> node?

Here is the XML:

<?xml version="1.0"?>
<document>
     <note>First note</note>
     <para>First paragraph</para>
     <note>Second note</note>
     <para>Second paragraph</para>
     <note>Third note</note>
     <note>Fourth note</note>
     <para>Third paragraph</para>
</document>

Here is the XSLT template for the <para> node:

<xsl:template match="para">
    <xsl:choose>
        <xsl:when test="local-name(preceding-sibling::*[1]) = 'note'">
            <xsl:variable name="current_para" select="."/>
              <group>
                <spara>
                   <xsl:apply-templates
                        select="preceding-sibling::note[following-sibling::para[1]=$current_para]"/>
                   <para><xsl:value-of select="."/></para>
                </spara>
              </group>
           </xsl:when>
        <xsl:otherwise>
           <group>
               <para><xsl:value-of select="."/></para>
           </group>
        </xsl:otherwise>
     </xsl:choose>
  </xsl:template>

Here is the output XML:

<?xml version="1.0"?>

<document>
  <group>
    <spara>
       <note>First note</note>
       <para>First paragraph</para>
    </spara>
  </group>
  <group>
    <spara>
       <note>Second note</note>
       <para>Second paragraph</para>
    </spara>
  </group>
  <group>
    <spara>
      <note>Third note</note>
      <note>Fourth note</note>
      <para>Third paragraph</para>
    </spara>
  </group>
</document>

The XPath “preceding-sibling::note” gives us everything that is prior to the current <para>.   The “secret sauce” here is that we are applying a filter to include only <para> nodes which have a “following-sibling::para” which matches the current <para> that we are processing.  If anyone has a more elegant solution, I would be interested in seeing it.