RE: [xsl] Cartesian product of sets of nodes

[Bartolomeo Nicolotti <bnicolotti@xxxxxxxxx>]

Hi,

I thought that the question was syntetic, but clear, and no example was
needed, sorry for misunderstanding.

In the input xml we've hotels with available rooms in respone to a
search criteria from the user, for example for "1 room for 2 people and
1 room for 3 people" one may obtain:

<h>
  <r type="double"/>  <!-- 2 people onebed-->
  <r type="twin"/>    <!-- 2 people separated beds-->
  <r type="triple/>   <!-- 3 people -->
</h>

In this format the rooms amog which one can choose are all together, one
can choose between the two combinations:

  <r type="double"/>  <!-- 2 people -->
  <r type="triple/>   <!-- 3 people -->

  <r type="twin"/>    <!-- 2 people -->
  <r type="triple/>   <!-- 3 people -->


In the output xml we need to have only the combinations that fits
exactly the user request, so something like

<h>
  <r type="double"/>  <!-- 2 people -->
  <r type="triple/>   <!-- 3 people -->
</h>
<h>
  <r type="twin"/>    <!-- 2 people -->
  <r type="triple/>   <!-- 3 people -->
</h>

So my idea is to group the rooms by number of people and then do all the
combinations of elements from each group, i.e. something like a
cartesian product.

I think that we can group the nodes fragmets in a variable

$s[1] --> "<r type="double"/>  <!-- 2 people -->
  <r type="twin"/>    <!-- 2 people -->"

$s[2] --><r type="triple/>   <!-- 3 people -->

then use a recursive template like this

<template name="combine-rooms">
<param name="rooms">
<for-each select="rooms[1]/room">
<!-- tranlate the single room and output -->
  <!-- obtain trailing rooms xml fragments, simples version:-->
  <value-of select="rooms[1]/room"/>
  <if test="count(rooms)>1">
    <variable name="etc-rooms" select="for $x in 2 to last(rooms) return
rooms[$x]"/>
       <call-template name="combine-rooms">
        <with-param name="rooms" select="$etc-rooms">
       </call-template>
  </if>
</for-each>
</funtion>

What do you think about this?

Many thanks

Bye





Il giorno ven, 28/08/2009 alle 18.42 +0100, Michael Kay ha scritto:
> > Hi,
> > 
> > we've a variable number of sets of nodes of variable 
> > carindinality grouped from incoming xml, 
> > 
> > S1, S2, S3, ... Sn
> > 
> > is there a way of obtaining the cartesian product
> > 
> > S1 x S2 x S3 x S4 x... Sn
> > 
> 
> I think it would be useful to explain what you mean by showing the XML input
> and the desired XML output.
> 
> My understanding is that "cartesian product" has a mathematical meaning, and
> a conventional usage when talking about the relational model, and they
> aren't the same. One doesn't see the term used much in relation to XML. In
> particular, I'm not sure how you would represent a "variable number of sets
> of nodes" in the XPath data model, unless the nodes all happen to be in the
> same tree.
> 
> Regards,
> 
> Michael Kay
> http://www.saxonica.com/
> http://twitter.com/michaelhkay 
> 
-- 
Bartolomeo Nicolotti
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