XSLT mapping and summing source children into a single target attribute - xslt-2.0

Question

I have a source document with XML structure similar to this:
<FOO>
<BAR>x</BAR>
<BAR>y</BAR>
<BAR>z</BAR>
</FOO>
My target XML must have an attribute with a number that represents the numerical sum of x, y and z. Where x = 1, y = 2 and z = 3
NOTE: The x, y and z are not actually numbers in the source document. They are letters and need to be mapped to the numbers that they represent first.
In this case, the target should look something like:
<Target Sum=6>
</Target>
Anyone have an XSLT example that would do what I need?
Thanks in advance

Answer 1

<?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" indent="yes"/>
<xsl:template match="/">
<Target Sum="{sum(FOO/BAR)}" />
</xsl:template>
EDIT:
This is a bit verbose, and there is probably a more elegant way to do it, but essentially I have a named template here that recursively calls itself to calculate the sum after the hard-coded mapping occurs:
<?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" indent="yes"/>
<xsl:template match="/">
<Target>
<xsl:attribute name="Sum">
<xsl:call-template name="GetSum">
<xsl:with-param name="CurrentNode" select="FOO/BAR[position()=1]"/>
</xsl:call-template>
</xsl:attribute>
</Target>
</xsl:template>
<xsl:template name="GetSum">
<xsl:param name="CurrentNode"/>
<xsl:param name="Number" select="0"/>
<xsl:variable name="Recursive_Result">
<xsl:variable name="MappedNumber">
<xsl:choose>
<xsl:when test="$CurrentNode/. = 'x'">1</xsl:when>
<xsl:when test="$CurrentNode/. = 'y'">2</xsl:when>
<xsl:when test="$CurrentNode/. = 'z'">3</xsl:when>
<xsl:otherwise>0</xsl:otherwise>
</xsl:choose>
</xsl:variable>
<!-- if there is a next sibling, recursively call GetSum -->
<xsl:choose>
<xsl:when test="$CurrentNode/following-sibling::BAR[1]">
<xsl:call-template name="GetSum">
<xsl:with-param name="CurrentNode" select="$CurrentNode/following-sibling::BAR[1]"/>
<xsl:with-param name="Number">
<xsl:value-of select="$MappedNumber"/>
</xsl:with-param>
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$MappedNumber"/>
</xsl:otherwise>
</xsl:choose>
</xsl:variable>
<!-- add the recursive_result to the number passed into the template. this will eventually build a sum -->
<xsl:value-of select="$Recursive_Result + $Number"/>
</xsl:template>
</xsl:stylesheet>

Answer 2

A much simpler, shorter and efficient solution:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:key name="kMap" match="#value" use="../#key"/>
<xsl:variable name="vMaps" as="element()*">
<map key="x" value="1"/>
<map key="y" value="2"/>
<map key="z" value="3"/>
</xsl:variable>
<xsl:template match="/*">
<Target Sum="{sum(key('kMap', BAR, document('')))}"/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the provided XML document:
<FOO>
<BAR>x</BAR>
<BAR>y</BAR>
<BAR>z</BAR>
</FOO>
the wanted, correct result is produced:
<Target Sum="6"/>
Explanation: Appropriate use of xsl:key, the 3rd argument of the key() function and AVT.