## RE: [xsl] sorting by comparing two nodes

 Subject: RE: [xsl] sorting by comparing two nodes From: "Michael Kay" Date: Wed, 21 Dec 2005 00:39:05 -0000
```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: [xsl] 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

```