Performing a “Group By” query in XPath XSL

Question

Given the following XML:

  11 
  

        

Answer 1

To do this in XSLT 1.0, you will have to use a technique called "muenchian grouping". First create a key of the nodes on which you wish to group

<xsl:key name="intfield" match="int" use="substring-before(@name, ':')" />

Next, you iterate it through all the nodes, but only selecting the ones that happen to be first in the relevant group

<xsl:for-each select="int[generate-id() = generate-id(key('intfield', substring-before(@name, ':'))[1])]">

Next, you can iterate use the key to iterate over all nodes in the group

<xsl:variable name="intfieldname" select="substring-before(@name, ':')"/>
<xsl:for-each select="key('intfield', $intfieldname)">

Putting this all together gives

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
   <xsl:output method="xml"/>
   <xsl:key name="intfield" match="int" use="substring-before(@name, ':')"/>
   <xsl:template match="/results">
      <results>
         <xsl:for-each select="int[generate-id() = generate-id(key('intfield', substring-before(@name, ':'))[1])]">
            <xsl:variable name="intfieldname" select="substring-before(@name, ':')"/>
            <field>
               <xsl:attribute name="name">
                  <xsl:value-of select="$intfieldname"/>
               </xsl:attribute>
               <xsl:for-each select="key('intfield', $intfieldname)">
                  <value>
                     <xsl:attribute name="name">
                        <xsl:value-of select="substring-after(@name, ':')"/>
                     </xsl:attribute>
                     <xsl:value-of select="."/>
                  </value>
               </xsl:for-each>
            </field>
         </xsl:for-each>
      </results>
   </xsl:template>
</xsl:stylesheet>

In your example, 'intfield' becomes 'numberfield' though. I have kept the name as 'intfield' in the above example.

• fixed typo.

Answer 2

Muenchian grouping is a work of genius. It's not easy to understand, but see: http://www.jenitennison.com/xslt/grouping/muenchian.html

To simplify the process the W3C specifically supported grouping in XSLT2.0. See, for example: http://www.xml.com/pub/a/2003/11/05/tr.html

However not all environments support XSLT2.0