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RE: Continuous path of elements satisfying a condition

2004-12-19 16:13:41

1) I can select the leaves and then all the relevant items with

<xsl:variable name="leaves" select="//item[(_at_)id and not(*) and 
not (ancestor::item[not(@id)])]"/>
<xsl:variable name="items" select="$leaves | $leaves/ancestor::item"/>

Is there a better way?

I don't think there is a more concise way, but there may be a more efficient
way.

You could change the second variable to

select="$leaves/ancestor-or-self::item"

but it's not a big difference.

You might get a performance benefit by going downwards only: this needs a
recursive function (and XSLT 2.0)

<xsl:function name="f:down">
  <xsl:param name="i" as="element(item)"/>
  <xsl:sequence select="if ($i/@id) then 
                          if (child::item) 
                             then for $x in child::item return f:down($x)
                             else $i
                          else ()"/>
</xsl:function>

If @id attributes occur infrequently, this will search a much smaller part
of the tree.


2) In the template for an item, I need to loop through the 
item's children that meet the
conditions (i.e., that are in $items).  I've tried this

<xsl:variable name="nitems" select="count($items)"/>

<xsl:template match="/">
<xsl:apply-templates select="$items"/>
</xsl:template>

<xsl:template match="item">
<xsl:for-each select="item[count(. | $items) = $nitems]">
      ...
</xsl:text>
</xsl:for-each>
</xsl:template>

This is fairly elegant but testing in my environment (MSXML) 
shows it to take 4 seconds
while a recursive template that just sums the number of 
included items that are 
children of the current item runs about 50 lines but takes 
half the time to run.


That doesn't surprise me. In XPath 2.0 you can do a set intersection
directly, as $A intersect $B. The XPath 1.0 workaround of $A[count(.|$B) =
count($B)] is likely to be pretty efficient unless the optimizer rewrites it
radically.

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


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