"sorted" axis (was: Remove duplicates from a node-set according to content)

[Sebastian Rahtz <sebastian.rahtz@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Jarno Elovirta writes:

 > I'm trying to find a way to remove duplicate nodes from a node-set
 > according to the content of the nodes, e.g. ignore all duplicate
 > reference elements whose name attribute is the same. 

Its not quite the same question, but related. My issue is the
processing of a sorted list, and extracting just the different
values. My data looks something like this:

<cemetery>
<stone>
 <person><name><fnm>Francis d'Arcy
   Godolphin</fnm><snm>Osborne</snm></name><died><date><day>20</day><mon>
   3</mon><yr>1964</yr></date></died></person>
 <person><name><fnm>Francis d'Arcy
   Another</fnm><snm>Osborne</snm></name><died><date><day>20</day><mon>
   3</mon><yr>1959</yr></date></died></person>
 <person><name><fnm>Francis d'Arcy
   TheLast/fnm><snm>Osborne</snm></name><died><date><day>20</day><mon>
   3</mon><yr>1964</yr></date></died></person>
<stone> ....
  <person>....
</cemetery>

that is to say, a set of <stone>s containing several <person>s who
have a <died> date. What I want to end up with is

 1959
   Another, Francis
 1964
   Godolphin, Francis
   TheLast, Francis

So, I can process the <person> elements sorted by died/date/yr, and by
name/snm. But when I come to the template that matches "person", which
receives this sorted node set, I cannot say things like "was the date
of the previous person the same as mine", because preceding and
following axes refer to the order of the _source_ tree.

This is really a question to those developing the XSL spec: is this a
reasonable requirement? or am I on the wrong side of the 80/20 divide?
is my vague hope for "sorted" axes doomed to disappointment?

Can anyone suggest good ways of solving the problem using what we
have now?  For those who are interested, David Carlisle _did_ find a nice
solution for me (data:
http://users.ox.ac.uk/~rahtz/xslcourse/data.xml, 
solution: http://users.ox.ac.uk/~rahtz/xslcourse/ex23.xsl) but it has
to use a little brute force and as a result is a trifle slow (it takes 
35 minutes to process a 2.5Mbyte input file --- I have only tried it
with XT, as it is written using July XSL syntax)

Sebastian



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