Update the counter by +1 when another record with two similar values exists in xslt 2.0 - counter

Question

I have the below xml:
<EmployeeLeaveDataUpsertRequest>
<Row>
<Emp_id>11</Emp_id>
<Pay_slip_no>1</Pay_slip_no>
<Pay_comp>AU_0299</Pay_comp>
<Hours>136</Hours>
<Date_from_ec>20170401</Date_from_ec>
<Date_to_ec>20170429</Date_to_ec>
<Date_ped> </Date_ped>
<No_of_period>1</No_of_period>
<Ma_ind>M</Ma_ind>
<Fa_ind>N</Fa_ind>
<Counter>1</Counter>
</Row>
<Row>
<Emp_id>12</Emp_id>
<Pay_slip_no>1</Pay_slip_no>
<Pay_comp>AU_0900</Pay_comp>
<Hours>40</Hours>
<Date_from_ec>20170206</Date_from_ec>
<Date_to_ec>20170210</Date_to_ec>
<Date_ped> </Date_ped>
<No_of_period>1</No_of_period>
<Ma_ind>M</Ma_ind>
<Fa_ind>N</Fa_ind>
<Counter>1</Counter>
</Row>
<Row>
<Emp_id>11</Emp_id>
<Pay_slip_no>1</Pay_slip_no>
<Pay_comp>AU_0299</Pay_comp>
<Hours>8</Hours>
<Date_from_ec>20170111</Date_from_ec>
<Date_to_ec>20170115</Date_to_ec>
<Date_ped> </Date_ped>
<No_of_period>1</No_of_period>
<Ma_ind>M</Ma_ind>
<Fa_ind>N</Fa_ind>
<Counter>1</Counter>
</Row>
In the above xml you can see that every record has an element counter with default value set as 1.
In an event for same Emp_id and Pay_comp then I need to set the counter as 1 for first record , 2 for second record and so on.
Like in the above xml you can see two records where the Emp_id is 11 and Pay_comp is AU_0299 -- so for the first one set the counter as 1 and for the next one a 2.
output xml:
<EmployeeLeaveDataUpsertRequest>
<Row>
<Emp_id>11</Emp_id>
<Pay_slip_no>1</Pay_slip_no>
<Pay_comp>AU_0299</Pay_comp>
<Hours>136</Hours>
<Date_from_ec>20170401</Date_from_ec>
<Date_to_ec>20170429</Date_to_ec>
<Date_ped> </Date_ped>
<No_of_period>1</No_of_period>
<Ma_ind>M</Ma_ind>
<Fa_ind>N</Fa_ind>
<Counter>1</Counter>
</Row>
<Row>
<Emp_id>11</Emp_id>
<Pay_slip_no>1</Pay_slip_no>
<Pay_comp>AU_0299</Pay_comp>
<Hours>8</Hours>
<Date_from_ec>20170111</Date_from_ec>
<Date_to_ec>20170115</Date_to_ec>
<Date_ped> </Date_ped>
<No_of_period>1</No_of_period>
<Ma_ind>M</Ma_ind>
<Fa_ind>N</Fa_ind>
<Counter>2</Counter>
</Row>
<Row>
<Emp_id>12</Emp_id>
<Pay_slip_no>1</Pay_slip_no>
<Pay_comp>AU_0900</Pay_comp>
<Hours>40</Hours>
<Date_from_ec>20170206</Date_from_ec>
<Date_to_ec>20170210</Date_to_ec>
<Date_ped> </Date_ped>
<No_of_period>1</No_of_period>
<Ma_ind>M</Ma_ind>
<Fa_ind>N</Fa_ind>
<Counter>1</Counter>
</Row>
I have tried for loop but couldn't succeed. Need your inputs on the XSLT code which could achieve it

Answer 1

You could use a key to identify duplicates, with XSLT 3.0 (as now supported by Saxon 9.8 or current versions of Altova XMLSpy and Raptor) it is as easy as:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:math="http://www.w3.org/2005/xpath-functions/math"
exclude-result-prefixes="xs math"
expand-text="yes"
version="3.0">
<xsl:key name="group" match="Row" use="Emp_id , Pay_comp" composite="yes"/>
<xsl:mode on-no-match="shallow-copy"/>
<xsl:template match="Row[not(. is key('group', (Emp_id , Pay_comp))[1])]/Counter">
<xsl:copy>{index-of(key('group', (../Emp_id , ../Pay_comp)), ..)}</xsl:copy>
</xsl:template>
</xsl:stylesheet>
With XSLT 2.0 you can translate the above to
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:math="http://www.w3.org/2005/xpath-functions/math"
exclude-result-prefixes="xs math"
version="2.0">
<xsl:key name="group" match="Row" use="concat(Emp_id, '|', Pay_comp)"/>
<xsl:template match="#* | node()">
<xsl:copy>
<xsl:apply-templates select="#* | node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="Row[not(. is key('group', concat(Emp_id, '|', Pay_comp))[1])]/Counter">
<xsl:copy>
<xsl:value-of select="index-of(key('group', concat(../Emp_id, '|', ../Pay_comp)), ..)"/>
</xsl:copy>
</xsl:template>