Re: [xsl] Question on duplicate node elimination

Subject: Re: [xsl] Question on duplicate node elimination
From: Michael Kay <mike@xxxxxxxxxxxx>
Date: Sun, 22 Aug 2010 22:53:28 +0100
I'm not sure what you find surprising about the results you are seeing. What results would you expect?

xsl:copy-of creates a new node. Copying the same node twice creates two copies with distinct identity. Is that the issue?

Michael Kay
Saxonica

On 22/08/2010 22:25, Hermann Stamm-Wilbrandt wrote:
Hello,

I have a question on duplicate node elimination.

> From the XPATH 1.0 specification:
...
* node-set (an unordered collection of nodes without duplicates)
...
An initial sequence of steps is composed together with a following step as
follows. The initial sequence of steps selects a set of nodes relative to a
context node. Each node in that set is used as a context node for the
following step. The sets of nodes identified by that step are unioned
together. The set of nodes identified by the composition of the steps is
this union.
...

So "are unioned together" results in a node-set and that does not contain
duplicates.

Now how can this algorithm step be realized in XPATH 1.0 plus
exslt:node-set
funtion?
(this would work in browsers with the technique from David Carlisle [1])


This is the output for below stylesheet simple.xsl on file simple.xml. For the nodes four node /a/b/c their parents are copied into an intermediate result. But xsltproc and xalan show that the four nodes are different by the their generate-id() values, whereas the first pair and last pair are representations of the same node.

xsltproc        xalan
1: id2659470    1: AbT0
2: id2659470    2: AbT0
3: id2659354    3: AbT1
4: id2659354    4: AbT1

1: id2659234    1: AbT2
2: id2659244    2: AbT3
3: id2659254    3: AbT4
4: id2659264    4: AbT5

1:<b>           1:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>
2:<b>           2:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>
3:<b>           3:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>
4:<b>           4:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>



$ cat simple.xml
<a>
<b>
<c>1</c>
<c>2</c>
</b>
<b>
<c>1</c>
<c>2</c>
</b>
</a>
$ cat simple.xsl
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
xmlns:exsl="http://exslt.org/common";
<xsl:output omit-xml-declaration="yes"/>

   <xsl:template match="/">
     <xsl:variable name="rtf">
       <xsl:for-each select="/a/b/c">
         <xsl:copy-of select=".."/>
       </xsl:for-each>
     </xsl:variable>

     <xsl:for-each select="/a/b/c">
       <xsl:value-of select="position()"/><xsl:text>:</xsl:text>
       <xsl:value-of select="generate-id(..)"/><xsl:text>&#10;</xsl:text>
     </xsl:for-each>

<xsl:text>&#10;</xsl:text>

     <xsl:for-each select="exsl:node-set($rtf)/*">
       <xsl:value-of select="position()"/><xsl:text>:</xsl:text>
       <xsl:value-of select="generate-id(.)"/><xsl:text>&#10;</xsl:text>
     </xsl:for-each>

<xsl:text>&#10;</xsl:text>

     <xsl:for-each select="exsl:node-set($rtf)/*">
       <xsl:value-of select="position()"/><xsl:text>:</xsl:text>
       <xsl:copy-of select="."/><xsl:text>&#10;</xsl:text>
     </xsl:for-each>
   </xsl:template>

</xsl:stylesheet>
$


[1] http://dpcarlisle.blogspot.com/2007/05/exslt-node-set-function.html



Mit besten Gruessen / Best wishes,


Hermann Stamm-Wilbrandt
Developer, XML Compiler, L3
WebSphere DataPower SOA Appliances
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