Removing duplicate edge elements

geoGregory3 · February 26th, 2008, 02:55 PM

Hi,
This is my first post here. I have the following:
<graph>
    <nodes>
    <node>A</node>
    <node>B</node>
    <node>C</node>
    <node>D</node>
    <node>E</node>
    </nodes>
    <edges>
    <edge source="A" dest="B"/>
    <edge source="A" dest="C"/>
    <edge source="A" dest="D"/>
    <edge source="D" dest="E"/>
    <edge source="A" dest="C"/>
    <edge source="C" dest="D"/>
    <edge source="A" dest="B"/>
    </edges>
</graph>

As you can see, there are duplicate edges (e.g. edges A --> B and A --> C occur twice). I'd like to know how I go about removing these duplicate edges using xslt 1.0 (or 2.0 if not possible in 1.0) such that I have the following:

<graph>
    <nodes>
    <node>A</node>
    <node>B</node>
    <node>C</node>
    <node>D</node>
    <node>E</node>
    </nodes>
    <edges>
    <edge source="A" dest="B"/>
    <edge source="A" dest="C"/>
    <edge source="A" dest="D"/>
    <edge source="D" dest="E"/>
    <edge source="C" dest="D"/>
    </edges>
</graph>

Thanks!

samjudson · February 27th, 2008, 05:23 AM

A simple (but depending on the number of items perhaps not the fastest) might be to do something like:

Code:

<xsl:for-each select="edge">
  <xsl:if test="empty(preceding-sibling::edge[@source=current()/@current and @dest=current()/@dest])">
    <xsl:copy-of select="."/>
  </xsl:if>
</xsl:for-each>

/- Sam Judson : Wrox Technical Editor -/

mhkay · February 27th, 2008, 06:08 AM

In XSLT 1.0, elimination of duplicates is best done using Muenchian grouping, see for example http://www.jenitennison.com/xslt/grouping. In XSLT 2.0 it's best done using the new xsl:for-each-group instruction.

Neither handles a composite grouping key directly; you will have to form this using string concatenation. For example in 2.0

<xsl:for-each-group select="edge" group-by="concat(@source, '~', @dest)">
<xsl:copy-of select="."/>
</xsl:for-each-group>

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference