Dynamic parameters for XSLT 2.0 group-by - dynamic

Question

I got this input
<?xml version="1.0" encoding="UTF-8"?>
<result>
<datapoint poiid="2492" period="2004" value="1240"/>
<datapoint poiid="2492" period="2005" value="1290"/>
<datapoint poiid="2492" period="2006" value="1280"/>
<datapoint poiid="2492" period="2007" value="1320"/>
<datapoint poiid="2492" period="2008" value="1330"/>
<datapoint poiid="2492" period="2009" value="1340"/>
<datapoint poiid="2492" period="2010" value="1340"/>
<datapoint poiid="2492" period="2011" value="1335"/>
<datapoint poiid="2493" period="2004" value="1120"/>
<datapoint poiid="2493" period="2005" value="1120"/>
<datapoint poiid="2493" period="2006" value="1100"/>
<datapoint poiid="2493" period="2007" value="1100"/>
<datapoint poiid="2493" period="2008" value="1100"/>
<datapoint poiid="2493" period="2009" value="1110"/>
<datapoint poiid="2493" period="2010" value="1105"/>
<datapoint poiid="2493" period="2011" value="1105"/>
</result>
and I use this xslt 2.0
<?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" exclude-result-prefixes="xs" version="2.0">
<xsl:output method="xml" indent="yes"/>
<xsl:template match="result">
<xsl:for-each-group select="datapoint" group-by="#poiid">
<node type="poiid" id="{#poiid}">
<xsl:for-each select="current-group()">
<node type="period" id="{#period}" value="{#value}"/>
</xsl:for-each>
</node>
</xsl:for-each-group>
</xsl:template>
</xsl:stylesheet>
to convert it into
<?xml version="1.0" encoding="UTF-8"?>
<node type="poiid" id="2492">
<node type="period" id="2004" value="1240"/>
<node type="period" id="2005" value="1290"/>
<node type="period" id="2006" value="1280"/>
<node type="period" id="2007" value="1320"/>
<node type="period" id="2008" value="1330"/>
<node type="period" id="2009" value="1340"/>
<node type="period" id="2010" value="1340"/>
<node type="period" id="2011" value="1335"/>
</node>
<node type="poiid" id="2493">
<node type="period" id="2004" value="1120"/>
<node type="period" id="2005" value="1120"/>
<node type="period" id="2006" value="1100"/>
<node type="period" id="2007" value="1100"/>
<node type="period" id="2008" value="1100"/>
<node type="period" id="2009" value="1110"/>
<node type="period" id="2010" value="1105"/>
<node type="period" id="2011" value="1105"/>
</node>
Works smoothly.
Where I got stuck is when I tried to make it more dynamic. The real life input has 6 attributes for each datapoint instead of 3, and the usecase requires the possibility to set the grouping parameters dynamically.
I tried using parameters
<xsl:param name="k1" select="'poiid'"/>
<xsl:param name="k2" select="'period'"/>
but passing them to the rest of the xslt is something that I can't get right. The code below doesn't work, but clarifies hopefully, what I'm looking for.
<xsl:template match="result">
<xsl:for-each-group select="datapoint" group-by="#{$k1}">
<node type="{$k1}" id="#{$k1}">
<xsl:for-each select="current-group()">
<node type="{$k2}" id="#{$k2}" value="{#value}"/>
</xsl:for-each>
</node>
</xsl:for-each-group>
</xsl:template>
Any help appreciated..

Answer 1

Here is how to do it:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>
<xsl:param name="k1" select="'poiid'"/>
<xsl:param name="k2" select="'period'"/>
<xsl:template match="result">
<xsl:for-each-group select="datapoint" group-by="#*[name()= $k1]">
<node type="{$k1}" id="{#*[name() = $k1]}">
<xsl:for-each select="current-group()">
<node type="{k2}" id="{#*[name()= $k2]}" value="{#value}"/>
</xsl:for-each>
</node>
</xsl:for-each-group>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the provided XML document:
<result>
<datapoint poiid="2492" period="2004" value="1240"/>
<datapoint poiid="2492" period="2005" value="1290"/>
<datapoint poiid="2492" period="2006" value="1280"/>
<datapoint poiid="2492" period="2007" value="1320"/>
<datapoint poiid="2492" period="2008" value="1330"/>
<datapoint poiid="2492" period="2009" value="1340"/>
<datapoint poiid="2492" period="2010" value="1340"/>
<datapoint poiid="2492" period="2011" value="1335"/>
<datapoint poiid="2493" period="2004" value="1120"/>
<datapoint poiid="2493" period="2005" value="1120"/>
<datapoint poiid="2493" period="2006" value="1100"/>
<datapoint poiid="2493" period="2007" value="1100"/>
<datapoint poiid="2493" period="2008" value="1100"/>
<datapoint poiid="2493" period="2009" value="1110"/>
<datapoint poiid="2493" period="2010" value="1105"/>
<datapoint poiid="2493" period="2011" value="1105"/>
</result>
the wanted, correct result is produced:
<node type="poiid" id="2492">
<node type="" id="2004" value="1240"/>
<node type="" id="2005" value="1290"/>
<node type="" id="2006" value="1280"/>
<node type="" id="2007" value="1320"/>
<node type="" id="2008" value="1330"/>
<node type="" id="2009" value="1340"/>
<node type="" id="2010" value="1340"/>
<node type="" id="2011" value="1335"/>
</node>
<node type="poiid" id="2493">
<node type="" id="2004" value="1120"/>
<node type="" id="2005" value="1120"/>
<node type="" id="2006" value="1100"/>
<node type="" id="2007" value="1100"/>
<node type="" id="2008" value="1100"/>
<node type="" id="2009" value="1110"/>
<node type="" id="2010" value="1105"/>
<node type="" id="2011" value="1105"/>
</node>