Aggregate-function for sum and product in XPath

Question

Similar to this question (http://stackoverflow.com/q/1333558/948404) I want to use XPath to calculate a sum over products in a structure like this:

<items>
    <item>
        <value>1.0</value>
        <quantity>3</quantity>
    </item>
    <item>
        <value>2.5</value>
        <quantity>2</quantity>
    </item>
    <!-- ... -->
</items>

Is there an XPath expression that calculates the sum of the products of each items value and quantity?

Update: The solution has to work with PHPs XSLTProcessor class meaning that it probably has to be XSLT 1.0 compliant. This is why I did not yet accept the two probably correct answers using XSLT 2.0. I could neither test them in my PHP implementation nor in my browser nor in the Tryit Editor [1] from w3schools. Sorry!

1. http://w3schools.com/xsl/tryxslt.asp?xmlfile=cdcatalog&xsltfile=cdcatalog

Answer 1

Use this XPath 2.0 expression:

sum(/items/item/(value * quantity))

Here is an XSLT 2.0 transformation as verification:

<xsl:stylesheet version="2.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="text"/>

    <xsl:template match="/">
        <xsl:sequence select="sum(/items/item/(value * quantity))"/>
    </xsl:template>
</xsl:stylesheet>

When this transformation is applied on the provided XML document:

<items>
    <item>
        <value>1.0</value>
        <quantity>3</quantity>
    </item>
    <item>
        <value>2.5</value>
        <quantity>2</quantity>
    </item>
    <!-- ... -->
</items>

the XPath expression is evaluated and the result of this evaluation is output:

8

Explanation:

In XPath 2.0 it is legal for a location step to be

/(expression),

or even

/someFunction(argumentList)

---

II. XSLT 1.0 solution:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:template match="/*">
  <xsl:call-template name="sumProducts">
    <xsl:with-param name="pNodes" select="item"/>
  </xsl:call-template>
 </xsl:template>

 <xsl:template name="sumProducts">
   <xsl:param name="pNodes" select="/.."/>
   <xsl:param name="pAccum" select="0"/>

   <xsl:choose>
    <xsl:when test="not($pNodes)">
     <xsl:value-of select="$pAccum"/>
    </xsl:when>
    <xsl:otherwise>
     <xsl:call-template name="sumProducts">
      <xsl:with-param name="pNodes" select="$pNodes[position() >1]"/>
      <xsl:with-param name="pAccum" select=
      "$pAccum + $pNodes[1]/value * $pNodes[1]/quantity"/>
     </xsl:call-template>
    </xsl:otherwise>
   </xsl:choose>
 </xsl:template>
</xsl:stylesheet>

when this transformation is applied on the provided XML document (above), again the wanted, correct result is produced:

8

Do note: Such kind of problems are easy to solve using the FXSL library. The template to call is transform-and-sum .