[xsl] Interesting problem: Combing tables sections into one table

["Ed Yau" <eyau@xxxxxxxxxxxxxxx>]

	Hi,

	I wanted to float this by everyone.  I have a very complicated
XSLT problem (imho), and want to seek opinions as to how best to proceed
with it.
	Hope someone's up for the challenge, as it baffles my relatively
small XSLT knowledge.

	I'm getting through XML from a data-extraction system that has
been used on phone bills.  The phone bills are normally folded in half
and stapled in middle in a booklet format.
	The XML looks something like this:

	<page no='3'>
	...
	<t-left>
	  <tr>
		<date> 26 Jan </date>
		<time> 11:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>  </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>27 Jan </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tf>
			... footer info ...
	 </tf>
	</t-left>
	...

	<t-right>
	  <tr>
		<date> 26 feb </date>
		<time> 11:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>  </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>27 feb </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tf>
			... footer info ...
	 </tf>
	</t-right>

	</page>

	<page no='4'>
	...
	<t-left>
	  <tr>
		<date> 28 Jan </date>
		<time> 11:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>  </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>29 Jan </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tf>
			... footer info ...
	 </tf>
	</t-left>
	...
	</page>

	What I am aiming for should look something like this:

	<table>
	  <tr>
		<date> 28 Jan </date>
		<time> 11:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>28 Jan   </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tr>
		<date>29 Jan </date>
		<time> 12:45 </time>
		<destination> XXX </destination>
	 </tr>
	  <tf>
			... footer info ...
	 </tf>
	</table>

	The two main challenges I'm faced with is therefore:
		1) reordering the entries as they should appear - the
order the appear in the XML is not the right order due to the folding
over the booklet
		2) filling 'empty' dates with preceeding dates

	I've considered the following approaches:
	1)  A 'pull' approach where I recurse over the tables bring them
together, doing the sorting.
		- The ordering of the pages is hard to predict.  There
is a pattern, but trying to code this in XSLT far defeats me.  I think
this is much the harder approach.
		The main problem I've found is that the way you recurse
depends on the total number of sections.  So I'd have to find some way
of counting this first.

	2) Trying to sort by date.  This is tricky because the months
are not in number format, and there are lots of missing dates that I'd
have to fill in at the same time.  I'm assuming it's possible to do this
as a 1-pass approach, but it would certainly be simpler as a 2-pass.

	Any thoughts on this welcome.  Anyone have any experience of
this?  Which approach do you think is likely to work best?

	Many thanks in advance,
		Ed