RE: [xsl] building a nodeset from selected nodes

[Wendell Piez <wapiez at mulberrytech dot com>]

At 09:23 PM 7/5/01, Kurt wrote:
>Hi Wendell,
>
>Using key() is sooooo much easier than recursive templates.
>
>At Thursday, July 05, 2001 8:52 AM, you wrote:
> > (Even if it didn't, you could still iterate over the column children and
> > use . for that second argument. ;-)
>
>I originally thought of doing this (assuming I understand you) but
>then I got back to the problem where I have multiple node-sets with
>no obvious (to me?) way to combine them into a single node-set, though
>I was eventually able to combine them using recursive template calls.

Well, that's effectively what key() is doing. What I was describing above 
is merely that we could say

<xsl:for-each select="column">
   <xsl:apply-templates select="key('columns-by-name', .)"/>
</xsl:for-each>

and be calling the function multiple times with the current column node's 
string value as the second argument each time.

But since we can do the same thing by putting the node-set itself into the 
second argument, this is unnecessary.

You also ask:
>Is there a simpler approach to combine a variable number of node-sets
>into a single node-set (without using extensions)?

Well, now we know how to do it with keys, it's easier to see how you could 
engineer your way back *out* of using them: so in your example, you could 
be doing

<xsl:template match="query">
   <xsl:variable name="matching-columns"
        select="//table/column[name=current()/column]"/>
   <xsl:for-each select="$matching-columns">
      ...
   </xsl:for-each>
</xsl:template>

and be binding the nodes into a variable that way. (This location path 
works because of the rule of what makes node-sets equal: that the string 
value of one of the nodes in the first node set equals the string value of 
one of the nodes in the other. Such a loose rule is useful sometimes.)

But even this is expensive compared to using keys, except maybe on small 
documents. It's really the key() function that's saving us all the work.

Cheers,
Wendell



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Wendell Piez                            mailto:wapiez@mulberrytech.com
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