Grouping by Month for a Symphony CMS Data Source Using Nils Hörrmann's Date and Time Field Extension

events.xml

<!--
	Snapshot of the XML I was working with.
-->
…
<event-listing>
    <section id="21" handle="event">Event</section>
    <entry id="100">
        <city handle="city">City</city>
        <date>
            <date timeline="1" type="range">
                <start iso="2011-07-06T00:00:00-05:00" time="00:00" weekday="3" offset="-0500">2011-07-06</start>
                <end iso="2011-07-09T04:00:00-05:00" time="04:00" weekday="6" offset="-0500">2011-07-09</end>
            </date>
        </date>
        <event-name handle="event-name-2">Event Name</event-name>
        <state handle="US">US</state>
        <url handle="http-wwwsiteorg">http://www.site.org/</url>
    </entry>
    <entry id="101">
        <city handle="city-2">City 2</city>
        <date>
            <date timeline="1" type="range">
                <start iso="2011-08-06T00:00:00-05:00" time="00:00" weekday="3" offset="-0500">2011-07-06</start>
                <end iso="2011-08-09T04:00:00-05:00" time="04:00" weekday="6" offset="-0500">2011-07-09</end>
            </date>
        </date>
        <event-name handle="event-name-2">Event Name 2</event-name>
        <state handle="US">US</state>
        <url handle="http-wwwsite2org">http://www.site2.org/</url>
    </entry>
</event-listing>
…

events.xslt

<?xml version="1.0" encoding="UTF-8"?>
<!--
	Created by Alex Lemanski on 2010-05-17.
-->
<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:import href="../utilities/Master.xsl"/>
  <!-- 
    Include the Format Date/Time Advanced Utility
    http://symphony-cms.com/download/xslt-utilities/view/20744/ 
  -->
  <xsl:import href="../utilities/Date-Time-Advanced.xsl"/>

  <xsl:template match="data">
    <article>
        <xsl:for-each select="event-listing/entry">
          <!-- 
            this test checks the first 7 characters from the string of
            `current()/date/date/start` and compares it with the one `event-item` node
            and inserts the appropriate month information when they are different
          -->
          <xsl:if test="substring(current()/date/date/start, 1, 7) != substring(preceding-sibling::entry[1]/date/date/start, 1, 7)">
            <h3>
              <span>
                <xsl:call-template name="format-date">
                  <xsl:with-param name="date" select="current()/date/date/start"/>
                  <xsl:with-param name="format" select="'%m+; %y+;'"/>
                </xsl:call-template>
              </span>
            </h3>
          </xsl:if>
          
          <article class='vevent'>
            <h4 class='summary'><xsl:value-of select="event-name"/></h4>
            <p class='dtstamp'>
              <abbr class='dtstart' title='{date/date/start}'>
                <xsl:call-template name="format-date">
                  <xsl:with-param name="date" select="date/date/start"/>
                  <xsl:with-param name="format" select="'%m+; %d;%ds;'"/>
                </xsl:call-template>
              </abbr>
              <xsl:if test="date/date/end != ''">
                <xsl:text>-</xsl:text>
                <abbr class='dtstart' title='{date/date/end}'>
                  <xsl:if test="substring(date/date/end, 6, 2) != substring(date/date/start, 6, 2)">
                    <xsl:call-template name="format-date">
                      <xsl:with-param name="date" select="date/date/end"/>
                      <xsl:with-param name="format" select="'%m+;'"/>
                    </xsl:call-template>
                    <xsl:text> </xsl:text>
                  </xsl:if>
                  <xsl:call-template name="format-date">
                    <xsl:with-param name="date" select="date/date/end"/>
                    <xsl:with-param name="format" select="'%d;%ds;'"/>
                  </xsl:call-template>
                </abbr>
              </xsl:if>
            </p>
            <p class='location'><xsl:value-of select="city"/>, <xsl:value-of select="state"/></p>
            <p class='description'><a href='{url}' target='_blank'><xsl:value-of select="substring-after(url,'//')"/></a></p>
          </article>
        </xsl:for-each>
      </div>
    </article>
  </xsl:template>
</xsl:stylesheet>