How can I sort values that have been calculated dynami

Hello,

This is connected to my earlier thread (Sorting a Nodeset contained within a
Variable), but as I haven't got that working I will try a more general
approach. Here goes:

My XML is a series of User elements structured as follows:

<User>
	<User_Name></User_Name>
	<Case_Code></Case_Code>
	<Case_Title></Case_Title>
	<Cost_Item>
		<User_ID></User_ID>
		<Job_Description></Job_Description>
		<Charge_Rate></Charge_Rate>
		<Item_Date></Item_Date>
		<Item_Description></Item_Description>
		<Time_Minutes></Time_Minutes>
		<Cost></Cost>
	</Cost_Item>	
  </User>

There may be a number of such entries with the same User_Name and a number
of those may have the same Case_Code and Case_Title. 

The desired output:
I am outputting a table with a series of columns, each of which has a
heading which, when clicked, will sort the table data according to the
heading clicked. 

Where I am at present:
Some of the columns contain data contained in the source XML (eg there are a
User_Name column and a Case_Code column); when these are clicked they are
sorting the data as required.

The problem:
Some of the columns contain data that is not directly in the source XML but
is computed from it (eg there is a column containing the total number of
unique Case_Code elements for each unique User_Name).  I have a template
matching each unique User_Name, and within this the data is being output
into the table using this code:

     <TH>
	<xsl:variable name="ThisUser" select="." />
     <xsl:value-of
select="count(//User[./User_Name=$ThisUser][not(Case_Code=preceding::Case_Co
de)])" />
     </TH>

 however, I have not been able to code the column heading so that it sorts
by this column when clicked.

Any suggestions as to how to go about this?

Bryan

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