How to find unmatched rows with XSLT - xslt

Question

I have two large xml files, one of which has the following format:
<Persons>
<Person>
<ID>1</ID>
<LAST_NAME>London</LAST_NAME>
</Person>
<Person>
<ID>2</ID>
<LAST_NAME>Twain</LAST_NAME>
</Person>
<Person>
<ID>3</ID>
<LAST_NAME>Dikkens</LAST_NAME>
</Person>
</Persons>
The second file has the following format:
<SalesPersons>
<SalesPerson>
<ID>2</ID>
<LAST_NAME>London</LAST_NAME>
</SalesPerson>
<SalesPerson>
<ID>3</ID>
<LAST_NAME>Dikkens</LAST_NAME>
</SalesPerson>
</SalesPersons>
I need to find those records from file 1, which does not exist in file 2. Although I have it done using for-each loop, such an approach is taking a substantial amount of time. Is it possible to somehow make it run faster using a different approach?

Answer 1

Using a key can help to improve performance on lookups:
<xsl:key name="sales-person" match="SalesPerson" use="concat(ID, '|', LAST_NAME)"/>
<xsl:template match="/">
<xsl:for-each select="Persons/Person">
<xsl:variable name="person" select="."/>
<!-- need to change context document for key function use -->
<xsl:for-each select="$doc2">
<xsl:if test="not(key('sales-person', concat($person/ID, '|', $person/LAST_NAME)))">
<xsl:copy-of select="$person"/>
</xsl:if>
</xsl:for-each>
</xsl:for-each>
</xsl:template>
That assumes you have bound doc2 as a variable or parameter with e.g. <xsl:param name="doc2" select="document('sales-persons.xml')"/>.