RE: [xsl] limiting preceding axis by ancestor

["Michael Kay" <michael dot h dot kay at ntlworld dot com>]

> I have a document where there are many instances of <foo>.
> Each <foo> may
> have many <bar> children.   <bar> is itself recursive to
> several levels.
>
> <foo>
> 	<bar>
> 	<bar>
> <foo>
> 	<bar>
> 		<bar>
> 			<bar>
>
> I want to test to see if any preceding <bar> has the same value as the
> current <bar> but limit the test to those <bar> elements are
> children of the
> immediate <foo> ancestor.

By "preceding" do you mean preceding in the sense of the preceding axis,
which excludes ancestors of the context node? I'll assume you do.

Using XPath 2.0 you could write

   preceding::bar intersect ancestor::foo//*

or

   preceding::bar except ancestor::foo/preceding::bar

If you do want to include ancestors of the context node, you could write

   ancestor::foo/descendant::bar[.<<current()]

which is probably going to be the most efficient as it's the only one that
doesn't look outside the foo subtree.

Several XSLT 1.0 processors have xx:intersect() and xx:difference()
extension functions which you could use to simulate the first two of these.

I can't immediately think of an XPath 1.0 solution that only looks in the
foo subtree. But there's an XSLT solution using xsl:number -

<xsl:variable name="thispos">
  <xsl:number level="any" from="foo"/>
</xsl:variable>

<xsl:for-each select="ancestor::foo//bar">
<xsl:variable name="thatpos">
  <xsl:number level="any" from="foo"/>
</xsl:variable>
<if test="$thatpos < $thispos">
  -- process this node --
</xsl:if>
</xsl:for-each>

Michael Kay
Software AG
home: Michael.H.Kay@ntlworld.com
work: Michael.Kay@softwareag.com




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