if test="position() = 1 or zip!=preceding-sibling::address[1]/zip" : proceding sibling « XPath « XML Tutorial

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2. XPath
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:if test="position() = 1 or zip!=preceding-sibling::address[1]/zip">
        <xsl:text>&#xA;Zip code </xsl:text>
        <xsl:value-of select="zip"/>
        <xsl:text> (</xsl:text>
        <xsl:value-of select="city"/>
        <xsl:text>, </xsl:text>
        <xsl:value-of select="state"/>
        <xsl:text>): &#xA;</xsl:text>
      </xsl:if>
      <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:template>
</xsl:stylesheet>

Output:


Zip code 48392 (New York, WI): 
Mr. Jack Smith
1234 Main Street