RE: grouping (was: if or template?)

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

(I wrote this post before finding Steve's example just now from Wednesday 
in my archive; I'll still post it since it is what I did this evening for 
myself to help me understand what he has developed. I think this is quite 
neat!)

At 00/05/08 17:54 +0100, Kay Michael wrote:
> > I want to then display the Tracker_ID if it is unique followed by all the
> data for
> > the specific tracker.
>
> A FAQ: use something like
> <xsl:for-each select="//tracker-id[not(.=preceding::tracker-id)]">
>
> This is the traditional solution; Steve Muench has just told me about a
> brilliant alternative using keys:
>
> <xsl:key name="tid" use="tracker-id" select="."/>
>
> <xsl:for-each
> select="//tracker-id[generate-id(.)=generate-id(key('tid',.)[1])]">
>
> I hope Steve will forgive me for announcing this discovery before he does,
> I'm quite excited by it because it gives much better performance.

This is a truly kewl idea ... but ... isn't the syntax above incorrect?

Wouldn't the declaration of the key be as follows?

    <xsl:key name="tid" match="tracker-id" use="."/>

I apologize in advance if this sounds pedantic, but readers might get 
confused about which attribute is the matching attribute (match=) and which 
is the selection (use=) since the cited example had it backwards and 
incorrectly named.

I have an example below.

I hope this helps.

................... Ken


T:\ftemp>type tests.xml
<?xml version="1.0"?>
<names>
<name><given>Julie</given><surname>Holman</surname></name>
<name><given>Margaret</given><surname>Mahoney</surname></name>
<name><given>Ted</given><surname>Holman</surname></name>
<name><given>John</given><surname>Mahoney</surname></name>
<name><given>Kathryn</given><surname>Holman</surname></name>
<name><given>Ken</given><surname>Holman</surname></name>
</names>
T:\ftemp>type tests.xsl
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
                version="1.0">

<xsl:output method="text"/>

            <!--prepare to examine all names valued by surname-->
<xsl:key name="surnames" match="name" use="surname"/>

<xsl:template match="/">                         <!--root rule-->
            <!--select only those name elements whose unique
                generated id is equal to the generated id of the
                first of the key members with the same surname-->
  <xsl:for-each
        select="//name[generate-id(.)=
                       generate-id(key('surnames',surname)[1])]">
    <xsl:value-of select="surname"/>     <!--show the grouping-->
    <xsl:text>&#xd;&#xa;</xsl:text>
                        <!--select only those for the grouping-->
    <xsl:for-each select="//name[surname=current()/surname]">
      <xsl:sort select="given"/>    <!--sorted within grouping-->
      <xsl:text>   </xsl:text>
      <xsl:value-of select="given"/>   <!--member distinctions-->
      <xsl:text>&#xd;&#xa;</xsl:text>
    </xsl:for-each>
  </xsl:for-each>
</xsl:template>

</xsl:stylesheet>

T:\ftemp>saxon tests.xml tests.xsl
Holman
   Julie
   Kathryn
   Ken
   Ted
Mahoney
   John
   Margaret


--
G. Ken Holman                    mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
Crane Softwrights Ltd.             http://www.CraneSoftwrights.com/s/
Box 266, Kars, Ontario CANADA K0A-2E0   +1(613)489-0999   (Fax:-0995)
Web site: XSL/XML/DSSSL/SGML services, training, libraries, products.
Practical Transformation Using XSLT and XPath      ISBN 1-894049-04-7
Next instructor-led training:               2000-05-11/12,2000-05-15,
-                                    2000-06-12,2000-06-13,2001-01-27


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