Problem using Muenchian Method

Hi,

I'm having a problem using the 'Muenchian Method' to produce unique output 
nodes. I'm sure it's not a problem with the method, just my fumbling 
application of it.

Here's the XML:

<?xml version='1.0' encoding='UTF-8'?>
<?xml-stylesheet href="test.xsl" type="text/xsl"?>

<categories>
        <category name='Duo'>
                <product id='W110'/>
                <product id='W111'/>
                <product id='W112'/>
        </category>
        <category name='Speciality'>
                <category name='Glass'>
                        <product id='W110'/>
                        <product id='W111'/>
                        <product id='W112'/>
                </category>
                <category name='Wood'>
                        <category name='Yew'>
                                <product id='W102'/>
                                <product id='W115'/>
                        </category>
                        <category name='Mahogany'>
                                <product id='W120'/>
                                <product id='W115'/>
                        </category>
                </category>
        </category>
</categories>

Here's the XSLT:

<?xml version="1.0" encoding="ISO-8859-1"?>

<xsl:stylesheet version="1.0" 
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>

        <xsl:output
                method="text"/>
        
        <xsl:key name="products-by-id" match="@id" use="."/>

        <xsl:param name="c"/>
        
        <xsl:variable name="cxpath" select="
                
/categories//category[(_at_)name=$c]//product[generate-id(@id)=generate-id(key('products-by-id',
 @id)[1])]
                "/>
        
        <xsl:variable name="xpath" select="
                
/categories/category//product[generate-id(@id)=generate-id(key('products-by-id',
 @id)[1])]
                "/>
        
        <xsl:variable name="newline">
                <xsl:text>
                
</xsl:text>
        </xsl:variable>

        <xsl:template match="/">
        
        <xsl:choose>
                <xsl:when test="$c">
                        <xsl:for-each select="$cxpath">
                                <xsl:value-of select="@id"/><xsl:value-of 
select="$newline"/>
                        </xsl:for-each>
                </xsl:when>
                <xsl:otherwise>
                        <xsl:for-each select="$xpath">
                                <xsl:value-of select="@id"/><xsl:value-of 
select="$newline"/>
                        </xsl:for-each>
                </xsl:otherwise>
        </xsl:choose>
                        
        </xsl:template>

</xsl:stylesheet>

Here's what I'm trying to do:

If no $c param is passed to the stylesheet, I want the output to be the @id 
attribute of every product node (but only once per unique @id). This works fine 
using the xpath expression held in $xpath.

If a $c param is passed to the stylesheet (the value of whuch will be identical 
to the @name attribute of any of the category nodes), I would like the output 
to be the @id attribute of every product node which is a descendant of the 
category node which has $c as the value of its @name attribute. But again, I 
would like the value of each unique @id output only once. The xpath for this is 
held in $cxpath.

This works for some nodes but not others. There is no problem if $c=Duo, 
$c=Wood or $c=Yew. But with other nodes, the output is either nothing at all, 
or some of the expected @ids are missing. This occurs if they have already 
appeared in the source xml document, or possibly because they have occured 
previously in the key.

Also, I know I have overused the xpath // . This has been mainly to simplify 
the above example.

Any help would be greatly appreciated. Thanks.

Pappa

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