RE: [xsl] Sorting Question: Muenchian method? Substring in Key?

["Michael Kay" <michael dot h dot kay at ntlworld dot com>]

There are two main approaches to grouping:

(a) the "not(x = preceding::x)" method
(b) the Muenchian method

Method (a) works only where the grouping key is the string-value of a
node; this is because it relies on the special properties of "=" when
comparing two node-sets. Where the grouping key is anything else (e.g.
the first character of the string value), you need to use Muenchian
grouping.

Michael Kay
Software AG
home: Michael.H.Kay@ntlworld.com
work: Michael.Kay@softwareag.com 

> -----Original Message-----
> From: owner-xsl-list@lists.mulberrytech.com 
> [mailto:owner-xsl-list@lists.mulberrytech.com] On Behalf Of Thomas_M
> Sent: 27 September 2002 16:27
> To: 'xsl-list@lists.mulberrytech.com'
> Subject: [xsl] Sorting Question: Muenchian method? Substring in Key?
> 
> 
> Hello. This is my first XSLT project. I'm having trouble with 
> grouping sorted items (seems to be a common theme). I have a 
> XML file like this
> (simplified):
> 
> <topics>
>   <topic>Anteater</topic>
>   <topic>Aardvark</topic>
>   <topic>Beetle, Smaller European Elm Bark</topic>
>   <topic>Beetle, American Burying</topic>
>   <topic>Chimpanzee</topic>
> </topics>
> 
> I would like the output to be sorted and grouped, with each 
> group getting a
> heading:
> 
> A
> Aardvark
> Anteater
> 
> B
> Beetle, American Burying
> Beetle, Smaller European Elm Bark
> 
> C
> Chimpanzee
> 
> The corresponding part of my XSL is below.
> 
>   <xsl:template match="topics">
>    <table border="1">
>       <xsl:for-each select="topic">
>         <xsl:sort select="."/>
>         <xsl:variable name="previndex" select="position()-1"/>
>         <xsl:if test="not(substring(.,1,1)
>                       = substring(/topics/topic[$previndex],1,1))">
> 		<tr><th><xsl:value-of 
> select="substring(.,1,1)"/></th></tr>
> 
>         </xsl:if>
>             <tr>
>               <td><xsl:value-of select="."/></td>
>             </tr>
>       </xsl:for-each>
>     </table>
>   </xsl:template> 
> 
> As you can see, I'm comparing an element in a sorted node-set 
> with a document-order node-set. This works only if the XML is 
> pre-sorted. Is there a way to create the sorted node-set 
> first, so that I can both traverse and use it in my test?
> 
> I have seen a few examples of the Muenchian method, and it 
> would seem this is another (perhaps better) way solve my 
> problem. However, I've tried several times to implement it 
> and can't seem to get it right (can you use a substring in a key?)
> 
> Thanks for any insight,
> 
> - Mark.
> 
> -- 
> Mark Thomas                       |_|
> Internet Systems Architect        -+-
> User Technology Associates, Inc.   |
> Thomas_M@bls.gov                  /-\
> 
> 
> 
> 
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