Use xsl:number together with xsl:for-each-group - xslt

Question

Consider the following XML document:
<cities>
<city name="Milano" country="Italia" pop="5"/>
<city name="Paris" country="France" pop="7"/>
<city name="München" country="Deutschland" pop="4"/>
<city name="Lyon" country="France" pop="2"/>
<city name="Venezia" country="Italia" pop="1"/>
</cities>
Using the above XML document and XSLT, I want to get the following output (desired output):
1.Country: Italia:
1.1. City: Milano
Population: 5 Millions
1.2. City: Venezia
Population: 1 Millions
total Population: 6 Millions
2.Country: France:
2.1. City: Paris
Population: 7 Millions
2.2 City: Lyon
Population: 2 Millions
total Population: 9 Millions
3.Country: Deutschland:
3.1 City: München
Population: 4 Millions
total Population: 4 Millions
Here is my attempt (it doesn't give me what i want to get):
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="2.0">
<xsl:template match="cities">
<xsl:for-each-group select="city" group-by="#country">
<xsl:number format="1."/>Country: <xsl:value-of select="current-grouping-key()"/>:
<xsl:for-each select="current-group()">
<!--<xsl:number count="current-group()|#name" format="1.1." level="multiple"/>: Error The current-group() function cannot be used in a pattern -->
City: <xsl:value-of select="#name" />
Population: <xsl:value-of select="#pop"/> Millions</xsl:for-each>
total Population: <xsl:value-of select="sum(current-group()/#pop)"/> Millions
</xsl:for-each-group>
</xsl:template>
</xsl:stylesheet>

Answer 1

xsl:number the way you tried mainly helps with numbering based on the input structure but perhaps the following suffices:
<xsl:template match="cities">
<xsl:for-each-group select="city" group-by="#country">
<xsl:number format="1." value="position()"/>Country: <xsl:value-of select="current-grouping-key()"/>:
<xsl:variable name="group-pos" select="position()"/>
<xsl:for-each select="current-group()">
<xsl:number value="$group-pos, position()" format="1.1." />: City: <xsl:value-of select="#name" />
Population: <xsl:value-of select="#pop"/> Millions
</xsl:for-each>
total Population: <xsl:value-of select="sum(current-group()/#pop)"/> Millions
</xsl:for-each-group>
</xsl:template>
Depending on the result format (like HTML) it might be easier to just construct nested ol/li lists and let them be numbered/styled with CSS.
Or create a temporary country/city hierarchy first for the xsl:numbering you had:
<xsl:template match="cities">
<xsl:variable name="countries">
<xsl:for-each-group select="city" group-by="#country">
<country name="{current-grouping-key()}" pop="{sum(current-group()/#pop)}">
<xsl:copy-of select="current-group()"/>
</country>
</xsl:for-each-group>
</xsl:variable>
<xsl:for-each select="$countries/country">
<xsl:number format="1."/>Country: <xsl:value-of select="#name"/>:
<xsl:for-each select="city">
<xsl:number level="multiple" format="1.1." count="country | city"/>: City: <xsl:value-of select="#name" />
Population: <xsl:value-of select="#pop"/> Millions
</xsl:for-each>
total Population: <xsl:value-of select="#pop"/> Millions
</xsl:for-each>
</xsl:template>