RE: [xsl] Re: Dynamic number of sort key component?

["Michael Kay" <mike@xxxxxxxxxxxx>]

Try something like this:

<xsl:function name="f:sort" as="element(row)*">
  <xsl:param name="data" as="element(row)"/>
  <xsl:param name="sortColumnNames" as="xs:string*"/>
  <xsl:param name="sortAscDesc" as="xs:string*"/>
  <xsl:variable name="sorted" as="element(row)">
    <xsl:perform-sort select="$data">
      <xsl:sort select="*[name()=$sortColumnNames[last()]" 
                order="{$sortAscDesc[last()]}" stable="yes"/>
    </xsl:perform-sort>
  <xsl:variable>
  <xsl:sequence select="if (count($sortColumnNames) eq 1 
                        then $sorted 
                        else f:sort($sorted, subsequence($sortColumnNames,
2), subsequence($sortAscDesc, 2))"/>
</xsl:function>

Those with grey hair will recognize this as the multi-phase sort process
used by punched card operators, sorting first by the last sort key, then the
last-but-one, and so on.

Regards,

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

> -----Original Message-----
> From: Fabre Lambeau [mailto:fabre.lambeau@xxxxxxxxx] 
> Sent: 14 May 2010 14:46
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [xsl] Re: Dynamic number of sort key component?
> 
> I'm writing a tool that allows my users to query an XML 
> document a-la-SQL (but simplified).
> For example, given an XML document such as:
> 
> <table>
>   <row>
>     <col name="a">1</col>
>     <col name="b">2</col>
>     <col name="c">3</col>
>     <col name="d">4</col>
>   </row>
>   <row>
>     <col name="a">bla</col>
>     <col name="b">bli</col>
>     <col name="c">blo</col>
>     <col name="d">blu</col>
>   </row>
>   <!-- ... -->
> </table>
> 
> I'd like them to be able to say something like:
> SELECT a,b,c,d
> ORDER BY a ASC,b DESC
> GROUP BY a,c,d
> 
> My component (XSLT stylesheet) takes that query and 
> effectively processes it in XSLT.
> The GROUP BY statement is easy to process, since I can just 
> concatenate the values for the corresponding <col> elements, 
> and use that string as a key to a for-each-group.
> However, I can't find a way to do the sorting (for which the 
> order is different for each individual column).
> 
> What I seem to need is the ability to have a dynamic number 
> of sort key components, which as far as I know is not 
> possible The following is obviously not possible:
> <xsl:perform-sort select="col">
>   <xsl:for-each select="tokenize($group-by, ',')">
>     <xsl:sort select="col[@name=string-before(current(),' ']) 
> order="{string-after(current(),' ']}ending"/>
>   </xsl:for-each>
> </xsl:perform>
> 
> Can anyone think of a way to do this (whilst retaining the 
> ability to have a dynamic list of ORDER BY columns, each one 
> specifying its own order)?
> Unfortunately, I don't think I have the ability to generate a 
> separate XSLT sheet after parsing the query string and 
> execute it, as my engine is all in XSLT (executed with AltovaXML)
> 
> --
> Fabre Lambeau