How to pattern match in XSLT and add values - xslt

Question

As part of an XSLT, I need to add all the values of the "Duration" element and display the value. Now, the below XML is a part of the larger XML I'm working on. In the below XML, I need to match
a/TimesheetDuration/Day*/Duration, add the values and display them. I dont want to store all the values in variables and add them. Is there any other clean way of doing this?
<?xml version="1.0" ?>
<a>
<TimesheetDuration>
<Day1>
<BusinessDate>6/12/2013</BusinessDate>
<Duration>03:00</Duration>
</Day1>
<Day2>
<BusinessDate>6/13/2013</BusinessDate>
<Duration>04:00</Duration>
</Day2>
<Day3>
<BusinessDate>6/14/2013</BusinessDate>
<Duration>05:00</Duration>
</Day3>
</TimesheetDuration>
</a>

Answer 1

An XPath 2.0 solution, assuming the durations are in the form HH:MM, would be
sum(for $d in a//Duration
return xs:dayTimeDuration(replace($d, '(..):(..)', 'PT$1H$2M')))

Answer 2

In xslt 1.0 you could do it for example with following stylesheet
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/">
<Durations>
<xsl:apply-templates select="a/TimesheetDuration/node()[starts-with(name(),'Day')]" />
<xsl:variable name="hours">
<xsl:call-template name="sumHours">
<xsl:with-param name="Day" select="a/TimesheetDuration/node()[starts-with(name(),'Day')][1]" />
</xsl:call-template>
</xsl:variable>
<SumOfHours>
<xsl:value-of select="$hours" />
</SumOfHours>
<!-- Sum of minutes would be calculated similarly -->
</Durations>
</xsl:template>
<xsl:template match="node()[starts-with(name(),'Day')]">
<xsl:copy-of select="Duration" />
</xsl:template>
<xsl:template name="sumHours">
<xsl:param name="tmpSum" select="0" />
<xsl:param name="Day" />
<xsl:variable name="newTmpSum" select="$tmpSum + substring-before($Day/Duration, ':')" />
<xsl:choose>
<xsl:when test="$Day/following-sibling::node()[starts-with(name(),'Day')]">
<xsl:call-template name="sumHours">
<xsl:with-param name="tmpSum" select="$newTmpSum" />
<xsl:with-param name="Day" select="$Day/following-sibling::node()[starts-with(name(),'Day')]" />
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$newTmpSum" />
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>
It produces output
<?xml version="1.0" encoding="UTF-8"?>
<Durations>
<Duration>03:00</Duration>
<Duration>04:00</Duration>
<Duration>01:00</Duration>
<SumOfHours>8</SumOfHours>
</Durations>