RE: [xsl] building a nodeset from selected nodes

Subject: RE: [xsl] building a nodeset from selected nodes
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Thu, 05 Jul 2001 17:18:27 +0100
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', .)"/>

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"
  <xsl:for-each select="$matching-columns">

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.


Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.      
17 West Jefferson Street                    Direct Phone: 301/315-9635
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