if test="not(preceding-sibling::address[zip=$lastZip])" : proceding sibling « XPath « XML Tutorial

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3. proceding sibling

File: Data.xml
<?xml version="1.0"?>
<addressbook>
  <address>
    <name>
      <title>Mr.</title>
      <first-name>Jack</first-name>
      <last-name>Smith</last-name>
    </name>
    <street>1234 Main Street</street>
    <city>New York</city>
    <state>WI</state>
    <zip>48392</zip>
  </address>
</addressbook>


File: Transform.xslt

<?xml version="1.0"?>
<xsl:stylesheet version="1.0" 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:output method="text" indent="no"/>

  <xsl:template match="/">
    <xsl:for-each select="addressbook/address">
      <xsl:sort select="zip"/>
      <xsl:variable name="lastZip" select="zip"/>
      <xsl:if test="not(preceding-sibling::address[zip=$lastZip])">
        <xsl:text>Zip code </xsl:text>
        <xsl:value-of select="zip"/>
        <xsl:text>: &#xA;</xsl:text>
        <xsl:for-each select="/addressbook/address[zip=$lastZip]">
          <xsl:sort select="name/last-name"/>
          <xsl:sort select="name/first-name"/>
          <xsl:if test="name/title">
            <xsl:value-of select="name/title"/>
            <xsl:text> </xsl:text>
          </xsl:if>
          <xsl:value-of select="name/first-name"/>
          <xsl:text> </xsl:text>
          <xsl:value-of select="name/last-name"/>
          <xsl:text>&#xA;</xsl:text>
          <xsl:value-of select="street"/>
          <xsl:text>&#xA;&#xA;</xsl:text>
        </xsl:for-each>
      </xsl:if>
    </xsl:for-each>
  </xsl:template>
</xsl:stylesheet>

Output:

Zip code 48392: 
Mr. Jack Smith
1234 Main Street