Calculating counts when working with elements using name/value pairs - xslt

Question

I have an xml in this format. I am looking to generate an output in the output format given below.
I am trying to calculate the total number of SkuID's associated with each unique SerialNum. The same SerialNum can be present more than once within the xml. Could you please suggest how I can get the count in this scenario?
<?xml version="1.0" encoding="UTF-8"?>
<root>
<Skid>
<NameValuePairs>
<NameValue>
<ID>SerialNum</ID>
<Value>12345678</Value>
</NameValue>
<NameValue>
<ID>calcTotals</ID>
<Value>true</Value>
</NameValue>
</NameValuePairs>
<Box>
<SkuID>5729305323</SkuID>
</Box>
<Box>
<SkuID>2334923423</SkuID>
</Box>
</Skid>
<Skid>
<NameValuePairs>
<NameValue>
<ID>SerialNum</ID>
<Value>22334455</Value>
</NameValue>
<NameValue>
<ID>calcTotals</ID>
<Value>true</Value>
</NameValue>
</NameValuePairs>
<Box>
<SkuID>42342234234</SkuID>
</Box>
<Box>
<SkuID>3243325352</SkuID>
</Box>
</Skid>
<Skid>
<NameValuePairs>
<NameValue>
<ID>SerialNum</ID>
<Value>12345678</Value>
</NameValue>
<NameValue>
<ID>calcTotals</ID>
<Value>true</Value>
</NameValue>
</NameValuePairs>
<Box>
<SkuID>75547453333</SkuID>
</Box>
<Box>
<SkuID>235356233266</SkuID>
</Box>
</Skid>
</root>
Output:
<Skids>
<Box>
<TrackingNumber>12345678</TrackingNumber>
<Total>4</Total>
</Box>
<Box>
<TrackingNumber>22334455</TrackingNumber>
<Total>2</Total>
</Box>
</Skids>

Answer 1

Using XSLT 2.0 with for-each-group
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
<xsl:output indent="yes"/>
<xsl:template match="root">
<Skids>
<xsl:for-each-group select="Skid" group-by="NameValuePairs/NameValue[ID='SerialNum']/Value">
<Box>
<TrackingNumber><xsl:value-of select=".//NameValue[ID='SerialNum']/Value"/></TrackingNumber>
<Total><xsl:value-of select="count(current-group()//Box)"/></Total>
</Box>
</xsl:for-each-group>
</Skids>
</xsl:template>
</xsl:stylesheet>
Using XSLT 1.0 with Muenchian Method
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:output indent="yes"/>
<xsl:key name="Tracking" match="Skid" use=".//NameValue[ID='SerialNum']/Value"/>
<xsl:template match="root">
<Skids>
<xsl:for-each select="Skid[generate-id() = generate-id(key('Tracking', .//NameValue[ID='SerialNum']/Value))]" >
<Box>
<TrackingNumber><xsl:value-of select=".//NameValue[ID='SerialNum']/Value"/></TrackingNumber>
<Total><xsl:value-of select="count(//Skid[.//NameValue[ID='SerialNum']/Value = current()//NameValue[ID='SerialNum']/Value]//Box)"/></Total>
</Box>
</xsl:for-each>
</Skids>
</xsl:template>
</xsl:stylesheet>
Output
<Skids>
<Box>
<TrackingNumber>12345678</TrackingNumber>
<Total>4</Total>
</Box>
<Box>
<TrackingNumber>22334455</TrackingNumber>
<Total>2</Total>
</Box>
</Skids>

Answer 2

The first part of my solution is a temporary variable, named ids,
and containing (no surprise) ID elements.
Each of them contains content of a Value element, which has ID sibling
with SerialNum content.
Additionally, this ID element has cnt attribute - the number of SkuID
elements in the "current" Skid.
Then ID elements in this variable are processed in a for-each-group loop,
grouping them by the content (ID value).
So the whole script looks like below:
<?xml version="1.0" encoding="UTF-8" ?>
<xsl:transform version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="UTF-8" indent="yes" />
<xsl:template match="root">
<Skids>
<xsl:variable name="ids">
<xsl:for-each select="//Value[../ID = 'SerialNum']">
<ID>
<xsl:attribute name="cnt" select="count(../../../Box/SkuID)"/>
<xsl:value-of select="."/>
</ID>
</xsl:for-each>
</xsl:variable>
<xsl:copy-of select="$ids"/>
<xsl:for-each-group select="$ids/ID" group-by=".">
<Box>
<ID><xsl:value-of select="."/></ID>
<Total><xsl:value-of select="sum(current-group()/#cnt)"/></Total>
</Box>
</xsl:for-each-group>
</Skids>
</xsl:template>
</xsl:transform>
Note: <xsl:copy-of select="$ids"/> instruction was placed for
demonstration purpose only. In the final version remove it.