[xsl] recursive sub-grouping

[Robin Wyles <rob@xxxxxxxxxxxxxx>]

Hi,

I am stuck on a transformation that requires me to group and sub-group 
a set of nodes based on their child nodes. My starting XML is as 
follows:

-------------- SOURCE ---------------
<?xml version="1.0"?>
<video-files>
	<video-file>
		<language>English</language>
		<format>Real</format>
		<bandwidth>Low</bandwidth>
	</video-file>
	<video-file>
		<language>English</language>
		<format>Real</format>
		<bandwidth>High</bandwidth>
	</video-file>
	<video-file>
		<language>English</language>
		<format>QuickTime</format>
		<bandwidth>Low</bandwidth>
	</video-file>
	<video-file>
		<language>English</language>
		<format>QuickTime</format>
		<bandwidth>High</bandwidth>
	</video-file>
	<video-file>
		<language>French</language>
		<format>Real</format>
		<bandwidth>Low</bandwidth>
	</video-file>
	<video-file>
		<language>French</language>
		<format>Real</format>
		<bandwidth>High</bandwidth>
	</video-file>
	<video-file>
		<language>French</language>
		<format>QuickTime</format>
		<bandwidth>Low</bandwidth>
	</video-file>
	<video-file>
		<language>French</language>
		<format>QuickTime</format>
		<bandwidth>High</bandwidth>
	</video-file>
</video-files>
-------------------------

And the final XML is to be as follows:

---------- FINAL ---------
<?xml version="1.0"?>
<languages>
	<language>
		<name>English</name>
		<formats>
			<format>
				<name>Real</name>
				<bandwidths>
					<bandwidth>
						<name>High</name>
					</bandwidth>
					[...]
				</bandwidths>				
			</format>
			[...]
		</formats>
	<language>
	[...]
</languages>
-----------------------------

I have searched the list for some pointers to a solution for this 
problem and I have found plenty on grouping and sub-grouping but I have 
had limited success in applying the techniques to my situation. The 
initial grouping of the languages is no problem, but I am not sure how 
to approach the sub-grouping on the current language group into format 
groups, and then sub-group each of these into the bandwidth groups. I 
have a feeling that I need to generate keys for the different 
language/format/bandwidth combinations, but I am not sure how to 
implement this. For what it's worth my current XSLT is as follows:

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

	<xsl:key name="languages" match="video-file" use="language"/>
	<xsl:key name="formats" match="video-file" use="concat(language, '+', 
format)"/>
	<xsl:key name="bandwidths" match="video-file" use="concat(language, 
'+', format, '+', bandwidth)"/>

	<xsl:template match="video-files">
		<languages>
			<xsl:for-each 
select="video-file[generate-id(.)=generate-id(key('languages', 
language)[1])]">
				<xsl:for-each select="key('languages', language)">
					<xsl:sort select="format"/>
					<language>
						<xsl:if test="position() = 1">
							<name><xsl:value-of select="language"/></name>
						</xsl:if>
						<formats>
							<!--- Need to do sub grouping here -->
						</formats>
					</language>
				</xsl:for-each>
			</xsl:for-each>
		</languages >
	</xsl:template>
</xsl:stylesheet>
--------------------------------

If anyone has any advice on the best way to approach this problem (XSLT 
1.0 only if possible), I would appreciate it.

Thanks,

Robin