Selecting distinct values from XSLT sub query - xslt

Question

I have this XML document:
<?xml version="1.0" encoding="UTF-8"?>
<metadata>
<properties>
<property name="prop1" type="type1"/>
<property name="prop2" type="type2"/>
<property name="prop3" type="type3"/>
<property name="prop4" type="type1"/>
</properties>
<types>
<type name="type1" group="group1"/>
<type name="type2" group="group1"/>
<type name="type3" group="group2"/>
<type name="type4" group="group3"/>
</types>
<groups>
<group name="group1" owner="owner1"/>
<group name="group2" owner="owner2"/>
<group name="group3" owner="owner3"/>
</groups>
</metadata>
I am transforming it using this XSLT:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<xsl:variable name="docRoot" select="/" />
<xsl:for-each select="distinct-values($docRoot/metadata/properties/property/#type)">
<xsl:variable name="groupOwner" select="$docRoot/metadata/groups/group[#name=$docRoot/metadata/types/type[#name=current()]/#group]/#owner" />
<xsl:value-of select="$groupOwner"/><xsl:text>
</xsl:text>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
What I want to do is print out the list of unique group owners for all of the properties in the document. I'm successfully filtering out duplicate types with distinct-values but can't see how to filter out duplicate owners.
The current output:
owner1
owner1
owner2
The required output:
owner1
owner2
If it helps no two groups have the same owner.

Answer 1

Keys can be your friend here...
<xsl:key name="types" match="type" use="#name" />
<xsl:key name="groups" match="group" use="#name" />
Then you can do this, without even any need for distinct-values because you won't get duplicate nodes returned this way:
<xsl:for-each select="key('groups', key('types', metadata/properties/property/#type)/#group)">
For example, try this XSLT
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" />
<xsl:key name="types" match="type" use="#name" />
<xsl:key name="groups" match="group" use="#name" />
<xsl:template match="/">
<xsl:for-each select="key('groups', key('types', metadata/properties/property/#type)/#group)">
<xsl:value-of select="concat(#owner, '
')" />
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
In fact, you can simplify the xsl:for-each to this:
<xsl:value-of select="key('groups', key('types', metadata/properties/property/#type)/#group)/#owner" separator="
" />

Answer 2

Ah, just needed to try a bit harder:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<xsl:variable name="docRoot" select="/" />
<xsl:for-each select="distinct-values($docRoot/metadata/groups/group[#name=$docRoot/metadata/types/type[#name=$docRoot/metadata/properties/property/#type]/#group]/#owner)">
<xsl:value-of select="current()"/><xsl:text>
</xsl:text>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
Open to any suggestions for simplifying this though!