Group by three common elements (XML to XML) - xslt-2.0

Question

We have a requirement in which we need to group by segments which are sharing three things common...I have attached the sample input and desire output..It would be great if someone help.
We need to make a group on the basis of Country, company name and Month of birth.
I have tried and I am beginner in this...so couldn't succeeded.
This is our input
<?xml version='1.0' encoding='utf-8'?>
<EMPDTLS>
<EMP>
<FIRST_NAME>John</FIRST_NAME>
<LAST_NAME>Mathew</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>DEC</MONTH_OF_BIRTH>
<COMPANY_NAME>TCS</COMPANY_NAME>
<BAND>B</BAND>
</EMP>
<EMP>
<FIRST_NAME>Luis</FIRST_NAME>
<LAST_NAME>Phillip</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>DEC</MONTH_OF_BIRTH>
<COMPANY_NAME>TCS</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>Nick</FIRST_NAME>
<LAST_NAME>Tatar</LAST_NAME>
<COUNTRY>USA</COUNTRY>
<MONTH_OF_BIRTH>JAN</MONTH_OF_BIRTH>
<COMPANY_NAME>CTS</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>Zuza</FIRST_NAME>
<LAST_NAME>Bark</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>JUNE</MONTH_OF_BIRTH>
<COMPANY_NAME>TCS</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>Jane</FIRST_NAME>
<LAST_NAME>ellis</LAST_NAME>
<COUNTRY>ENGLAND</COUNTRY>
<MONTH_OF_BIRTH>JUNE</MONTH_OF_BIRTH>
<COMPANY_NAME>IBM</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>SANJAY</FIRST_NAME>
<LAST_NAME>BAWARI</LAST_NAME>
<COUNTRY>ENGLAND</COUNTRY>
<MONTH_OF_BIRTH>JUNE</MONTH_OF_BIRTH>
<COMPANY_NAME>IBM</COMPANY_NAME>
<BAND>B</BAND>
</EMP>
<EMP>
<FIRST_NAME>Akhi</FIRST_NAME>
<LAST_NAME>Mahe</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>SEPT</MONTH_OF_BIRTH>
<COMPANY_NAME>IBM</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>Vishh</FIRST_NAME>
<LAST_NAME>Bombard</LAST_NAME>
<COUNTRY>GERMANY</COUNTRY>
<MONTH_OF_BIRTH>OCT</MONTH_OF_BIRTH>
<COMPANY_NAME>IBM</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>Sharon</FIRST_NAME>
<LAST_NAME>Watson</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>JULY</MONTH_OF_BIRTH>
<COMPANY_NAME>CTS</COMPANY_NAME>
<BAND>B</BAND>
</EMP>
<EMP>
<FIRST_NAME>Poo</FIRST_NAME>
<LAST_NAME>Smith</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>SEPT</MONTH_OF_BIRTH>
<COMPANY_NAME>CTS</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>John</FIRST_NAME>
<LAST_NAME>Smith</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>DEC</MONTH_OF_BIRTH>
<COMPANY_NAME>TCS</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
</EMPDTLS>
<Desired Output>
<?xml version='1.0' encoding='utf-8'?>
<EMPDTLS>
<EmpGrp>
<EMP>
<FIRST_NAME>John</FIRST_NAME>
<LAST_NAME>Mathew</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>DEC</MONTH_OF_BIRTH>
<COMPANY_NAME>TCS</COMPANY_NAME>
<BAND>B</BAND>
</EMP>
<EMP>
<FIRST_NAME>Luis</FIRST_NAME>
<LAST_NAME>Phillip</LAST_NAME>
<COUNTRY>INDIA</COUNTRY>
<MONTH_OF_BIRTH>DEC</MONTH_OF_BIRTH>
<COMPANY_NAME>TCS</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
</EmpGrp>
<EmpGrp>
<EMP>
<FIRST_NAME>Nick</FIRST_NAME>
<LAST_NAME>Tatar</LAST_NAME>
<COUNTRY>USA</COUNTRY>
<MONTH_OF_BIRTH>JAN</MONTH_OF_BIRTH>
<COMPANY_NAME>CTS</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
</EmpGrp>
<EmpGrp>
<EMP>
<FIRST_NAME>Jane</FIRST_NAME>
<LAST_NAME>ellis</LAST_NAME>
<COUNTRY>ENGLAND</COUNTRY>
<MONTH_OF_BIRTH>JUNE</MONTH_OF_BIRTH>
<COMPANY_NAME>IBM</COMPANY_NAME>
<BAND>A</BAND>
</EMP>
<EMP>
<FIRST_NAME>SANJAY</FIRST_NAME>
<LAST_NAME>BAWARI</LAST_NAME>
<COUNTRY>ENGLAND</COUNTRY>
<MONTH_OF_BIRTH>JUNE</MONTH_OF_BIRTH>
<COMPANY_NAME>IBM</COMPANY_NAME>
<BAND>B</BAND>
</EMP>
</EmpGrp>
**

Answer 1

Composite grouping keys are a bit easier in XSLT 3 (the latest version of XSLT since the summer of 2017 and supported by Saxon 9.8 or 9.9 as well as Altova 2017 or 2018 or 2019) as there you can use e.g. for-each-group composite="yes" group-by="COUNTRY, COMPANY_NAME, MONTH_OF_BIRTH":
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="#all"
version="3.0">
<xsl:mode on-no-match="shallow-copy"/>
<xsl:output indent="yes"/>
<xsl:template match="EMPDTLS">
<xsl:copy>
<xsl:for-each-group select="EMP" composite="yes" group-by="COUNTRY, COMPANY_NAME, MONTH_OF_BIRTH">
<EmpGrp>
<xsl:copy-of select="current-group()"/>
</EmpGrp>
</xsl:for-each-group>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
You can test it online at https://xsltfiddle.liberty-development.net/jyRYYhU/1.
As for XSLT 2, see https://cranesoftwrights.github.io/books/ptux/index.htm for a thorough treatment of XSLT if you have no other text book available or also see the spec https://www.w3.org/TR/xslt20/#grouping-examples which has "A Composite Grouping Key" as the second example by nesting for-each-group. Another technique in XSLT 2 is to concatenate the various items composing the grouping key to a string e.g. group-by="string-join((COUNTRY, COMPANY_NAME, MONTH_OF_BIRTH), '|')", making sure the separator character (e.g. |) is not contained in any key item value.