Sum two elements by grouping using XSLT 2.0 - xslt-2.0

Question

I'm trying to sum two elements "amount" and "retroAmount" group by "tmid" using xslt 2.0 and I tried two methods, in method-1 everything is stacking up and in the method-2 it displays NaN. Any ideas about how this can be fixed?
Here is my XML file:
<?xml version="1.0" encoding="UTF-8"?>
<Request xmlns:env="http://schemas.xmlsoap.org/soap/envelope/">
<row>
<tmid>abc</tmid>
<amount>651.03</amount>
<retroAmount>0</retroAmount>
</row>
<row>
<tmid>abc</tmid>
<amount>250.75</amount>
<retroAmount>-10</retroAmount>
</row>
<row>
<tmid>abc</tmid>
<amount>132</amount>
<retroAmount>-16.1</retroAmount>
</row>
<row>
<tmid>xyz</tmid>
<amount>129.19</amount>
<retroAmount>49.96</retroAmount>
</row>
<row>
<tmid>xyz</tmid>
<amount>148.76</amount>
<retroAmount>0</retroAmount>
</row>
<row>
<tmid>xyz</tmid>
<amount>92.29</amount>
<retroAmount>12</retroAmount>
</row>
</Request>
Output I am expecting:
<top xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Results>
<tmId>abc</tmId>
<total>1007.68</total>
</Results>
<Results>
<tmId>xyz</tmId>
<total>432.2</total>
</Results>
</top>
Any help is appreciated.
The XSLT code I was playing with:
Method-1 (everything is stacking up or being displayed without summing)
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema" version="2.0">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/">
<root>
<xsl:for-each-group select="Request/row"
group-by="tmid">
<row>
<tmid>
<xsl:value-of
select="current-grouping-key()"
/>
</tmid>
<xsl:for-each-group select="current-group()" group-by=".">
<amount>
<xsl:value-of select="sum(number(current-group()/amount))"/>
</amount>
<retroamount>
<xsl:value-of select="sum(number(current-group()/retroAmount))"/>
</retroamount>
</xsl:for-each-group>
</row>
</xsl:for-each-group>
</root>
</xsl:template>
</xsl:stylesheet>
Method-2 (I was only using "amount" and still it is displaying NaN, I would like to sum up both "amount" and "retroAmount"
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema" version="2.0">
<xsl:output method="xml" omit-xml-declaration="yes" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="/*">
<top>
<xsl:for-each-group select="//tmid" group-by=".">
<Results>
<tmId>
<xsl:sequence
select="current-grouping-key()"
/>
</tmId>
<total>
<xsl:sequence select="sum(number(current-group()/amount))"/>
</total>
</Results>
</xsl:for-each-group>
</top>
</xsl:template>
</xsl:stylesheet>

Answer 1

You basically want
<xsl:template match="Request">
<xsl:copy>
<xsl:for-each-group select="row" group-by="tmid">
<Results>
<tmId>{current-grouping-key()}</tmId>
<total>{sum(current-group()!(amount, retroAmount))}</total>
</Results>
</xsl:for-each-group>
</xsl:copy>
</xsl:template>
(that is XSLT 3 with XPath 3.1 syntax, but in XSLT 2 with XPath 2 syntax you would use
<xsl:template match="Request">
<xsl:copy>
<xsl:for-each-group select="row" group-by="tmid">
<Results>
<tmId>
<xsl:value-of select="current-grouping-key()"/>
</tmId>
<total>
<xsl:value-of select="sum(current-group()/(amount, retroAmount))"/>
</total>
</Results>
</xsl:for-each-group>
</xsl:copy>
</xsl:template>
I only later noticed that the Request element is meant to be transformed to a top element so change the <xsl:template match="Request"><xsl:copy>...</xsl:copy></xsl:template> from above suggestions to <xsl:template match="Request"><step>...</step></xsl:template>.