XSLT1.0: remove duplicates combined with an xsl:key

Question

I have the following piece of XML:

<research>
  <research.record>
    <research.record_number>1</research.record_number>
    <research.type>
      <value lang="en-US">some research type</value>
    </research.type>
    <research.type>
      <value lang="en-US">some other type of research</value>
    </research.type>
    <project.record>
      <priref>101</priref>
      <project.type>
        <value lang="en-US">some type of project</value>
      </project.type>
    </project.record>
  </research.record>
</research>
<research>
  <research.record>
    <research.record_number>2</research.record_number>
    <research.type>
      <value lang="en-US">some other type of research</value>
    </research.type>
    <research.type>
      <value lang="en-US">a third type of research</value>
    </research.type>
    <project.record>
      <priref>101</priref>
      <project.type>
        <value lang="en-US">some type of project</value>
      </project.type>
    </project.record>
  </research.record>
</research>
<research>
  <research.record>
    <research.record_number>3</research.record_number>
    <research.type>
      <value lang="en-US">some other type of research</value>
    </research.type>
    <research.type>
      <value lang="en-US">a fourth type</value>
    </research.type>
    <project.record>
      <priref>201</priref>
      <project.type>
        <value lang="en-US">some other type of project</value>
      </project.type>
    </project.record>
  </research.record>
</research>
<research>
   ... etc ...

With XSLT 1.0 I transform this XML into a list of unique project records by using xsl:key.

So far, so good...

The problem is: I also want to show unique research types for each unique project record.

My simplified stylesheet which shows the repeated research.types (but not unique ones)

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl">

  <xsl:output method="html" indent="yes"/>

  <xsl:key name="uniqueProject" match="project.record" use="priref"/>

  <xsl:template match="record">
    <div class="table-row">
    <xsl:apply-templates select="//project.record[generate-id() = generate-id(key('uniqueProject', priref)[1])]">
        <xsl:sort select="startdate"/>
    </xsl:apply-templates>
    </div>
   </xsl:template>

   <xsl:template match="project.record">
     <div class="project-container">
       <xsl:text>project.record </xsl:text>
       <xsl:value-of select="priref"/>
       <xsl:text>: </xsl:text>
       <xsl:for-each select="//research/research.record/research.type[../project.record/priref = current()/priref]"> 
         <xsl:sort select="value[@lang='en-US']" data-type="text" />         
           <xsl:if test="value[@lang='en-US'][not(.=preceding::research/research.record/research.type/value[@lang='en-US'][../../project.record/priref = current()/priref])]">
             <xsl:value-of select="value[@lang='en-US']"/>
           </xsl:if>
           <xsl:if test="position()!=last()">
             <xsl:text>, </xsl:text>
           </xsl:if>
         </xsl:for-each>
       </div>
       <br/>
       <br/>
    </xsl:template>

</xsl:stylesheet>

My wanted output would be:

project.record 101: some research type, some other type of research, a third type of    research

project.record 201: some other type of research, a fourth type

Hope someone can help me out with the right XSLT/XPATH. (Can only use XSLT1.0)

Answer 1

I would approach this by using a second key that groups research.type values by a combination of their value and their associated priref.

<xsl:key name="resTypeKey" match="research.type/value[@lang='en-US']"
    use="concat(., '+++', ../../project.record/priref)" />

and then use the same Muenchian trick as you already have for the table rows:

<xsl:template match="project.record">
  <div class="project-container">
    <xsl:text>project.record </xsl:text>
    <xsl:value-of select="priref"/>
    <xsl:text>: </xsl:text>
    <xsl:apply-templates select="
      key('uniqueProject', priref)/../research.type
        /value[@lang='en-US'][
          generate-id() = generate-id(
           key('resTypeKey', concat(., '+++', current()/priref))[1])]">
      <xsl:sort select="." />
    </xsl:apply-templates>
  </div>
  <br/>
  <br/>
</xsl:template>

<xsl:template match="research.type/value">
  <xsl:if test="position() &gt; 1">, </xsl:if>
  <xsl:value-of select="."/>
</xsl:template>