Verticalize XML using XSLT - xslt

Question

I am trying to implement an at first looking simple transformation but whatever I have tried has been failed.
The XML is generated from a fixed length record and have the below format.
<?xml version="1.0" encoding="UTF-8"?>
<record>
<no_of_records>30</no_of_records>
<cust_lastname_1>Smith</cust_lastname_1>
<cust_name_1>John</cust_name_1>
<cust_id_1>X45</cust_id_1>
<cust_lastname_2>George</cust_lastname_2>
<cust_name_2>Michael</cust_name_2>
<cust_id_2>X76</cust_id_2>
<cust_lastname_3>Ria</cust_lastname_3>
<cust_name_3>Chris</cust_name_3>
<cust_id_3>C87</cust_id_3>
...
</record>
The no_of_records indicates how many _X suffixed elements contains each record and because of its fix length origin has a defined maximum.
I want to transform it to a “verticalized” form resempling the below.
<record>
<customer num="1">
<lastname>Smith</lastname>
<name>John</name>
<id>X45</id>
</customer>
<customer num="2">
<lastname>George</lastname>
<name>Michael</name>
<id>X76</id>
</customer>
<customer num="3">
<lastname>Ria</lastname>
<name>Chris</name>
<id>C87</id>
...
</customer>
</record>
Any help would greatly appreciated.

Answer 1

In XSLT 2.0, you want something like
<xsl:for-each-group select="*" group-starting-with="*[starts-with(local-name(), 'cust_lastname']">
<customer num="{position()}">
<xsl:apply-templates select="current-group()"/>
</customer>
</xsl:for-each-group>
....
<xsl:template match="*[starts-with(local-name(), 'cust')]">
<xsl:element name="{replace(local-name(), 'cust_(.*?)_[0-9]+', '$1')}">
<xsl:value-of select="."/>
</xsl:element>
</xsl:template>

Answer 2

The solution from #Michael Kay works fine. Thank you !
XML
<?xml version="1.0" encoding="UTF-8"?>
<record>
<no_of_records>3</no_of_records>
<cust_lastname_1>Smith</cust_lastname_1>
<cust_name_1>John</cust_name_1>
<cust_id_1>X45</cust_id_1>
<cust_lastname_2>George</cust_lastname_2>
<cust_name_2>Michael</cust_name_2>
<cust_id_2>X76</cust_id_2>
<cust_lastname_3>Ria</cust_lastname_3>
<cust_name_3>Chris</cust_name_3>
<cust_id_3>C87</cust_id_3>
</record>
XSLT
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="record">
<records>
<xsl:for-each-group select="*[starts-with(local-name(), 'cust_')]"
group-starting-with="*[starts-with(local-name(), 'cust_lastname')]">
<customer num="{position()}">
<xsl:apply-templates select="current-group()"/>
</customer>
</xsl:for-each-group>
</records>
</xsl:template>
<xsl:template match="*[starts-with(local-name(), 'cust')]">
<xsl:element name="{replace(local-name(), 'cust_(.*?)_[0-9]+', '$1')}">
<xsl:value-of select="."/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
Result
<?xml version="1.0" encoding="UTF-8"?>
<records>
<customer num="1">
<lastname>Smith</lastname>
<name>John</name>
<id>X45</id>
</customer>
<customer num="2">
<lastname>George</lastname>
<name>Michael</name>
<id>X76</id>
</customer>
<customer num="3">
<lastname>Ria</lastname>
<name>Chris</name>
<id>C87</id>
</customer>
</records>