As part of a new framework enhancement, I needed a method to ensure that certain DITA elements carried unique @id values. Our authoring tool does a good job identifying duplicate @id values within a topic, but does not indicate whether those values also exist in other topics referenced in the DITA map.

In this case, the best fit was to add a new check to the QA plugin.

The check should:

• Identify duplicate @id values on specific elements
• Return only distinct values (i.e. if 123 appears several times, then return 123 only once)

After some forum research, my first thought was to use a key match.

<xsl:key name="duplicateIds" match="elementName" use="@id" />

And reference it with

key('duplicateIds',@id)[2] and count(.|key('duplicateIds', @id)[1]) = 1

So the if statement for the check looked like

<xsl:for-each select="//parentElement">
<xsl:if test="key('duplicateIds',@id)[2] and count(.|key('duplicateIds', @id)[1]) = 1">
Remove duplicate elementName @id=<xsl:value-of select="@id"/>
</xsl:if>
</xsl:for-each>

Even though it met my requirements, it’s still an outdated approach that didn’t leave me with a job-well-done sense of completion. I wanted a cleaner solution that fit somewhere closer to the 2.0 realm.

I decided to use grouping to identify each distinct @id value. Then I could wrap an if statement to test for any groups that contained a second (duplicate) item. The result:

<xsl:for-each-group select="//elementName" group-by="@id">
<xsl:if test="current-group()[2]">
Remove duplicate elementName @id=<xsl:value-of select="@id"/>
</xsl:if>
</xsl:for-each-group>

Have a better approach? Leave a comment.