XSLT: merging files but with better performance of the process - xslt

Question

I have two XML files and desire a merger, the criterion for this merger is as follows:
nodes1.xml file content:
<nodes>
<node>
<type>a</type>
<name>joe</name>
</node>
<node>
<type>b</type>
<name>sam</name>
</node>
<node>
<type>c</type>
<name>pez</name>
</node>
<node>
<type>g</type>
<name>lua</name>
</node>
<node>
<type>a</type>
<name>tol</name>
</node>
<node>
<type>c</type>
<name>jua</name>
</node>
</nodes>
nodes2.xml file content:
<nodes>
<node>
<type>a</type>
<name>jill</name>
</node>
<node>
<type>c</type>
<name>imol</name>
</node>
<node>
<type>h</type>
<name>teli</name>
</node>
<node>
<type>f</type>
<name>jopp</name>
</node>
<node>
<type>c</type>
<name>zolh</name>
</node>
</nodes>
and by my xsl template I get:
<?xml version="1.0" encoding="UTF-8"?>
<nodes>
<node tipo="a">
<name>joe</name>
<name>tol</name>
<name>jill</name>
</node>
<node tipo="c">
<name>pez</name>
<name>jua</name>
<name>imol</name>
<name>zolh</name>
</node>
<node tipo="h">
<name>teli</name>
</node>
<node tipo="f">
<name>jopp</name>
</node>
</nodes>
I need a solution to get better performance.
My current solution is:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:variable name="Source2" select="document('nodes2.xml')/nodes/node"/>
<xsl:variable name="Source1" select="document('nodes1.xml')/nodes/node"/>
<xsl:template match="/nodes" >
<nodes>
<xsl:for-each-group select="node" group-by="type">
<node tipo="{type}">
<xsl:apply-templates select="$Source1[type=current-grouping-key()]/name"/>
<xsl:apply-templates select="$Source2[type=current-grouping-key()]/name"/>
</node>
</xsl:for-each-group>
</nodes>
</xsl:template>
<xsl:template match="name">
<name><xsl:value-of select="."/></name>
</xsl:template>
</xsl:stylesheet>
I run it with java saxon:
$ java net.sf.saxon.Transform nodes2.xml mysolution.xsl
I think "a shame" to have the input file at the same time in a variable, but I can not figure out to do it differently.
I appreciate help or pointer.
--Paulino

Answer 1

Assuming you have the second of the files as the primary input to the XSLT code you can use the following:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes"/>
<xsl:param name="source1-uri" select="'nodes1.xml'"/>
<xsl:variable name="doc1" select="doc($source1-uri)"/>
<xsl:key name="by-type" match="nodes/node" use="type"/>
<xsl:template match="/nodes" >
<nodes>
<xsl:for-each-group select="key('by-type', node/type, $doc1), node" group-by="type">
<node tipo="{current-grouping-key()}">
<xsl:copy-of select="for $n in current-group() return $n/name"/>
</node>
</xsl:for-each-group>
</nodes>
</xsl:template>
</xsl:stylesheet>
I am not sure whether the order of the merged name elements matters to you but to ensure with Saxon 9.5 that I get the order you posted in your result sample I had to use <xsl:copy-of select="for $n in current-group() return $n/name"/> instead of the shorter and more usual <xsl:copy-of select="current-group()/name"/>.
So that solution should be more efficient, mainly by grouping on all input nodes and of course by then simply making use of current-group() instead of select the nodes again with a predicate.