How to create subsets of a single set of elements with XSLT?

Question

Hi all,

I have an xml of the form:

<Set>
   <Element name="Superset1_Set1_Element1"/>
   <Element name="Superset1_Set1_Element2"/>
   <Element name="Superset1_Set2_Element1"/>
   <Element name="Superset2_Set1_Element1"/>
   <Element name="Superset2_Set2_Element1"/>
</Set>

I wish to transform it to an xml of the form:

<Superset name="Superset1">
   <Set name="Set1">
       <Element name="Element1"/>
       <Element name="Element2"/>
   </Set>
   <Set name="Set2">
       <Element name="Element1"/>
   </Set>
</Superset>
<Superset name="Superset2">
   <Set name="Set1">
       <Element name="Element1"/>
   </Set>
   <Set name="Set2">
       <Element name="Element1"/>
   </Set>
</Superset>

How can this be done with XSLT?

Thanks a lot in advance!

Answer 1

Preserved for reference, but I strongly suggest the use of templates (i.e. Tomalak's solution) where possible for readability alone...

---

Certainly possible, but actually harder than I anticipated because of the second order sets and the double underscores - the following could certainly be improved if the "name" values were of a friendlier format.

<xsl:key name="supers" match="Set/Element" use="substring-before(@name,'_')"/>
<xsl:key name="sets" match="Set/Element" use="concat(substring-before(@name,'_'),'_',substring-before(substring-after(@name,'_'),'_'))"/>

<xsl:template match="/">
    <xsl:for-each select="Set/Element[generate-id() = generate-id(key('supers',substring-before(@name,'_'))[1])]">  
     <xsl:variable name="super" select="substring-before(@name,'_')"/>
      <Superset name="{$super}">   
      <xsl:for-each select="//Set/Element[generate-id() = generate-id(key('sets',concat($super,'_',substring-before(substring-after(@name,'_'),'_')))[1])]">
      <Set name="{substring-before(substring-after(@name,'_'),'_')}">
       <xsl:variable name="set" select="concat($super,'_',substring-before(substring-after(@name,'_'),'_'))"/>
       <xsl:for-each select="//Set/Element[starts-with(@name,$set)]">
        <Element name="{substring-after(substring-after(@name,'_'),'_')}"/>
       </xsl:for-each>
      </Set>
      </xsl:for-each>
      </Superset>
    </xsl:for-each>
</xsl:template>

The trick is just muenchian grouping and capturing the right key values.

It's really not pretty, so I'm sure there's a better solution available but I'm jetlagged :P