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Grouping with group-by

Using xsl:for-each-group element, sequences can be grouped by the specified criterion. The select attribute on xsl:for-each-group specifies sequences to be grouped, the second attribute on this element determines the type of grouping.

In this example nodes are grouped by the value of "v" attribute. For this kind of grouping attribute group-by is used.

Inside xsl:for-each-group select attribute of xsl:apply-template which is set to "." selects the first node of the group.

Function current-group() is used if all nodes from the group are needed. Function current-grouping-key() gives the grouping value which is currently used.

XSLT

      <xsl:stylesheet
                  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                  version="2.0">
            <xsl:output  method="xml"
                        indent="yes"
                        omit-xml-declaration="yes"/>

            <xsl:template  match="/aaa">
                  <xsl:for-each-group  select="*"
                              group-by="@v">
                        <sss>
                              <xsl:apply-templates  select="."/>
                        </sss>
                        <ggg  id="{current-grouping-key()}">
                              <xsl:apply-templates  select="current-group()"/>
                        </ggg>
                  </xsl:for-each-group>
            </xsl:template>

            <xsl:template  match="*">
                  <xsl:copy-of  select="."/>
            </xsl:template>

      </xsl:stylesheet>
XML

      <aaa>
            <bbb  v="a2"/>
            <ccc  v="1"/>
            <ddd  v="1"/>
            <eee  v="a2"/>
            <fff  v="1"/>
            <ggg  v="zz3"/>
      </aaa>
Output

      <sss>
            <bbb  v="a2"/>
      </sss>
      <ggg  id="a2">
            <bbb  v="a2"/>
            <eee  v="a2"/>
      </ggg>
      <sss>
            <ccc  v="1"/>
      </sss>
      <ggg  id="1">
            <ccc  v="1"/>
            <ddd  v="1"/>
            <fff  v="1"/>
      </ggg>
      <sss>
            <ggg  v="zz3"/>
      </sss>
      <ggg  id="zz3">
            <ggg  v="zz3"/>
      </ggg>


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