xsl:sort requires an expression that delivers a scalar value on which you
can sort; there's no way of sorting by specifying a comparator function that
compares any two values.

However, I'm sure FXSL could be used to rustle up such a higher-order sort()
function that takes a comparator function as an operand.

However, assuming your comparator function is transitive then I would think
there is almost certainly some function of a point that delivers a scalar
value on which you can sort directly.

Michael Kay
http://www.saxonica.com/


> -----Original Message-----
> From: Claus Nagel [mailto:claus.nagel@xxxxxxxxx] 
> Sent: 19 December 2005 21:05
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject:  sorting by comparing two nodes
> 
> Hi,
> I'm stuck with a sorting problem and hope to find some help here :-)
> 
> I have the following input:
> 
> <points>10 13,20 34,2 10,40 67</points>
> 
> This is a comma-separated list of 2d points. Each point consists of a
> x-coordinate and a y-coordinate, parted by a white-space.
> 
> And I have a reference point, eg.
> 
> <refpoint>3 2</refpoint>
> 
> Now I want to sort the list of points. To do so I have to compare two
> points and compute the following:
> result = (P1.x - P0.x)*(P2.y - P0.y) - (P2.x - P0.x)*(P1.y - P0.y)
> 
> (P0 -> reference point,
>  P1 -> one point of the list,
>  P2 -> another point of the list)
> 
> According to the value of "result", P1 and P2 shall be sorted 
> as follows:
> 
>  result < 0: P1 goes before P2
>  result > 0: P2 goes before P1
>  result = 0: no sorting required
> 
> Assume the following template:
> <xsl:template name="sort">
>   <xsl:with-param name="refpoint"/>
>   <xsl:with-param name="$points"/>
>     <xsl:for-each select="tokenize($points,',')">
>       <xsl:sort select="."/>
>       ......
>     </xsl:for-each>
> </xsl:template>
> 
> I can't compare two points within <xsl:sort/> the way I have to, can
> I? How can I solve my sorting problem using xslt?
> 
> Thanks for any ideas,
> Claus