RE: Creating a hierarchal unordered list from flat fil

David:

I have a solution to your problem...

Given that your source Document is: (I had to fix it)
<Root>
  <Groups GroupID="1" Name="Group1" ParentID="0"/>
  <Groups GroupID="2" Name="Group2" ParentID="1"/>
  <Groups GroupID="3" Name="Group3" ParentID="1"/>
  <Groups GroupID="4" Name="Group4" ParentID="1"/>
  <Groups GroupID="5" Name="Group5" ParentID="2"/>
  <Groups GroupID="6" Name="Group6" ParentID="2"/>
  <Groups GroupID="7" Name="Group7" ParentID="3"/>
  <Groups GroupID="8" Name="Group8" ParentID="3"/>
  <Groups GroupID="9" Name="Group9" ParentID="4"/>
  <Groups GroupID="10" Name="Group10" ParentID="5"/>
  <Groups GroupID="11" Name="Group11" ParentID="5"/>
  <Groups GroupID="12" Name="Group12" ParentID="6"/>
  <Groups GroupID="13" Name="Group13" ParentID="8"/>
  <Groups GroupID="14" Name="Group14" ParentID="8"/>
  <Groups GroupID="15" Name="Group15" ParentID="9"/>
  <Groups GroupID="16" Name="Group16" ParentID="10"/>
  <Groups GroupID="17" Name="Group17" ParentID="10"/>
  <Groups GroupID="18" Name="Group18" ParentID="16"/>
  <Groups GroupID="19" Name="Group19" ParentID="18"/>
  <Groups GroupID="20" Name="Group20" ParentID="19"/>
</Root>

If you apply the following stylesheet:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   <xsl:template match="/">
     <root>
         <xsl:apply-templates select="/Root/Groups[@ParentID=0]"/>
      </root>
   </xsl:template>
   <xsl:template match="Groups">
      <xsl:copy>
         <xsl:apply-templates select="@*"/>
         <xsl:apply-templates
select="../Groups[@ParentID=current()/@GroupID]"/>
      </xsl:copy>
   </xsl:template>
   <xsl:template match="@*">
      <xsl:copy/>
   </xsl:template>
</xsl:stylesheet>

You should get the following results:
<root>
   <Groups GroupID="1" Name="Group1" ParentID="0">
      <Groups GroupID="2" Name="Group2" ParentID="1">
         <Groups GroupID="5" Name="Group5" ParentID="2">
            <Groups GroupID="10" Name="Group10" ParentID="5">
               <Groups GroupID="16" Name="Group16" ParentID="10">
                  <Groups GroupID="18" Name="Group18" ParentID="16">
                     <Groups GroupID="19" Name="Group19" ParentID="18">
                        <Groups GroupID="20" Name="Group20" ParentID="19"/>
                     </Groups>
                  </Groups>
               </Groups>
               <Groups GroupID="17" Name="Group17" ParentID="10"/>
            </Groups>
            <Groups GroupID="11" Name="Group11" ParentID="5"/>
         </Groups>
         <Groups GroupID="6" Name="Group6" ParentID="2">
            <Groups GroupID="12" Name="Group12" ParentID="6"/>
         </Groups>
      </Groups>
      <Groups GroupID="3" Name="Group3" ParentID="1">
         <Groups GroupID="7" Name="Group7" ParentID="3"/>
         <Groups GroupID="8" Name="Group8" ParentID="3">
            <Groups GroupID="13" Name="Group13" ParentID="8"/>
            <Groups GroupID="14" Name="Group14" ParentID="8"/>
         </Groups>
      </Groups>
      <Groups GroupID="4" Name="Group4" ParentID="1">
         <Groups GroupID="9" Name="Group9" ParentID="4">
            <Groups GroupID="15" Name="Group15" ParentID="9"/>
         </Groups>
      </Groups>
   </Groups>
</root>

There are a few things that you may need to think about. Currently a root
node of 0 is a fixed value. It should be possible to use a variable to
figure out which ParentID refers to the root node. Its simply a matter of
finding the ParentID for which there is no matching GroupID. Given that you
may have some errors and accidentally include two ParentIDs for which there
are no GroupIDs you may need to be a little devious about how you make the
choice...

But it works. 
Adam

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