Re: [xsl] Re: Re: A question about the expressive power and limitations of XPath 2.0

[Jeni Tennison <jeni at jenitennison dot com>]

Hi Dimitre,

>> OK, let me think... a higher-order distinct function is an example.
>> You have structured identifiers of the form "group.subgroup" and
>> you want to return a unique set of nodes based on the "group" part
>> of the identifier (note that Mike said they were discussion how to
>> support this already, so perhaps there'll be a new 'distinct'
>> clause added to the for expression to solve it). A recursive
>> solution would be:
>> 
>> <xsl:function name="my:distinct">
>>   <xsl:param name="nodes" type="node*" select="()" />
>>   <xsl:param name="distinct" type="node*" select="()" />
>>   <xsl:variable name="new-distinct"
>>     select="if ($nodes[1] and
>>                 some $n in ($distinct)
>>                 satisfies (substring-before($n/@id, '.') =
>>                            substring-before($nodes[1]/@id, '.')))
>>             then ($distinct | $n)
>>             else $distinct" />
>>   <xsl:result select="if ($nodes)
>>                       then my:distinct($nodes[position() > 2],
>>                                        $new-distinct)
>>                       else $distinct
>> </xsl:function>
>
> I'm sorry, but it's not absolutely obvious. Let's have an example:

Sorry. I was imagining $nodes contains:

  <function id="str.concat">...</function>
  <function id="regexp.match">...</function>
  <function id="math.power">...</function>
  <function id="math.sin">...</function>
  <function id="str.tokenize">...</function>
  <function id="str.pad">...</function>

You need to group the functions by the initial part of their @id, and
get back a sequence of function elements that have unique values for
that part of their @id.

You can do it if you're generating a result using xsl:for-each-group:

  <xsl:for-each-group select="function"
                      group-by="substring-before(@id, '.')">
    ...
  </xsl:for-each-group>

But this doesn't help if you need to get hold of the function elements
themselves (because you need to select the first two in document
order, for example).

Cheers,

Jeni

---
Jeni Tennison
http://www.jenitennison.com/


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