Using muenchian grouping to select distinct values in a subtree - xslt

Question

I know how to do muenchian grouping but that normally is applied to a whole document (?).
Here I want to find distinct values in subtrees.
e.g.
<root>
<parent>
<child id="1"/>
<child id="1"/>
<child id="2"/>
</parent>
<parent>
<child id="2"/>
<child id="3"/>
<child id="3"/>
</parent>
</root>
I want to map to
<root>
<parent>
<child id="1"/>
<child id="2"/>
</parent>
<parent>
<child id="2"/>
<child id="3"/>
</parent>
</root>
If I try
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
>
<xsl:output method="xml" indent="yes"/>
<xsl:key name="id_to_id" match="/root/parent/child" use="#id"/>
<xsl:template match="/root">
<root>
<xsl:for-each select="parent">
<parent>
<xsl:for-each select="child[generate-id() = generate-id(key('id_to_id',#id)[1])]">
<child id="{#id}"/>
</xsl:for-each>
</parent>
</xsl:for-each>
</root>
</xsl:template>
</xsl:stylesheet>
then it does the key over the whole document and I get
<root>
<parent>
<child id="1" />
<child id="2" />
</parent>
<parent>
<child id="3" />
</parent>
</root>

Answer 1

So actually I've just created a solution but its a bit odd, ie generate an id for the parent node, and effectively we have a composite key of id attribute + id for the node
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
>
<xsl:output method="xml" indent="yes"/>
<xsl:key name="id_to_id" match="/root/parent/child" use="concat(#id,'|',generate-id(..))"/>
<xsl:template match="/root">
<root>
<xsl:for-each select="parent">
<parent>
<xsl:for-each select="child[generate-id() = generate-id(key('id_to_id',concat(#id,'|',generate-id(..)))[1])]">
<child id="{#id}"/>
</xsl:for-each>
</parent>
</xsl:for-each>
</root>
</xsl:template>
</xsl:stylesheet>
is this the standard way to do this sort of thing?

Answer 2

heres another equally bizarre solution, still not sure this is very sensible, is there some sort of XPath parenthesis or something I can use?
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
>
<xsl:output method="xml" indent="yes"/>
<xsl:key name="id_to_id" match="child" use="#id"/>
<xsl:template match="/root">
<root>
<xsl:for-each select="parent">
<parent>
<xsl:variable name="children">
<xsl:copy-of select="child"/>
</xsl:variable>
<xsl:for-each select="msxsl:node-set($children)/child[generate-id() = generate-id(key('id_to_id',#id)[1])]">
<child id="{#id}"/>
</xsl:for-each>
</parent>
</xsl:for-each>
</root>
</xsl:template>
</xsl:stylesheet>

Answer 3

now without meunchian grouping (which isnt what I want, but its a nice declarative approach), not suitable for anything but small groups of siblings.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
>
<xsl:output method="xml" indent="yes"/>
<xsl:template match="/root">
<root>
<xsl:for-each select="parent">
<parent>
<xsl:for-each select="child[not(#id = preceding-sibling::child/#id)]">
<child id="{#id}"/>
</xsl:for-each>
</parent>
</xsl:for-each>
</root>
</xsl:template>
</xsl:stylesheet>