local grouping

Hi all,

I have a grouping problem like this:

<g>
    <line x="1"/>
    <line x="2"/>
</g>
<g>
    <line x="1"/>
    <line x="1"/>
    <line x="2"/>
</g>

and so on..

For each <g> element I want to group the children into sub elements
based on the value of x, so like this:

<g>
    <g>
        <line x="1"/>
    </g>
    <g>
        <line x="2"/>
    </g>
</g>
<g>
    <g>
        <line x="1"/>
        <line x="1"/>
    </g>
    <g>
        <line x="2"/>
    </g>
</g>

I'm able to do this using the Muenchian Method and the extension
function intersection(). When I come across a <g> I want to iterate
across each possible x value that its children have and create a child
<g> for each one. So the code looks like this:

<xsl:key name="mykey" match="line" use="@x"/>

<xsl:template match="g">
    <xsl:variable name="children" select="child::*"/>
    <xsl:for-each
select="child::*[count(.|xalan:intersection(key(mykey, @x,
$children)[1]) = 1]">
       <!-- build the inner g's -->
    </xsl:for-each>
</xsl:template>

This works, but it is extremely slow. Does anyone have a more
efficient/faster way of doing this? It seems like it would be a common
problem, but I couldn't find any info about it.

Thanks,
Konrad