Creating taxonomic structure from individual records - xslt

Question

I am having a failure of imagination in how to effectively solve this problem. My actual data set has thousands of thousands of records. Each record indicates its location in a taxonomic structure. I need to create that taxonomic structure and place the records within that structure (e.g., records that indicate they go in "/a/b/c" end up in the "/a/b/c" but there is only one each of the taxonomic levels "a", "b", and "c"). Due to client confidentiality, I've posted a naive representation of this here.
Using XSLT 3 is desirable. I know there is a solution to this using xsl:iterate but I cannot figure it out.
Input:
<outer>
<record>
<id>rec1</id>
<taxNodes>
<node>
<id>1</id>
<note>First level</note>
<node>
<id>node2a</id>
<note>Second level Entry A</note>
</node>
</node>
</taxNodes>
</record>
<record>
<id>rec3</id>
<taxNodes>
<node>
<id>1</id>
<note>First level</note>
<node>
<id>node2b</id>
<note>Second level Entry B</note>
</node>
</node>
</taxNodes>
</record>
<record>
<id>rec4</id>
<taxNodes>
<node>
<id>1</id>
<note>First level</note>
<node>
<id>node2b</id>
<note>Second level Entry B</note>
</node>
</node>
</taxNodes>
</record>
</outer>
Desired Output:
<outer>
<node>
<id>1</id>
<note>First level</note>
<node>
<id>node2a</id>
<note>Second level Entry A</note>
<records>
<record>
<id>rec1</id>
</record>
</records>
</node>
<node>
<id>node2b</id>
<note>Second level Entry B</note>
<records>
<record>
<id>rec3</id>
</record>
<record>
<id>rec4</id>
</record>
</records>
</node>
</node>
</outer>

Answer 1

I think this can be seen as a grouping problem and then solved using a recursive function using xsl:for-each-group:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:math="http://www.w3.org/2005/xpath-functions/math"
xmlns:mf="http://example.com/mf"
exclude-result-prefixes="xs math mf"
version="3.0">
<xsl:output indent="yes"/>
<xsl:function name="mf:group" as="node()*">
<xsl:param name="input-nodes" as="element(node)*"/>
<xsl:for-each-group select="$input-nodes" group-by="id">
<xsl:copy>
<xsl:copy-of select="id, note"/>
<xsl:choose>
<xsl:when test="current-group()/node">
<xsl:sequence select="mf:group(current-group()/node)"/>
</xsl:when>
<xsl:otherwise>
<records>
<xsl:apply-templates select="current-group()/ancestor::record"/>
</records>
</xsl:otherwise>
</xsl:choose>
</xsl:copy>
</xsl:for-each-group>
</xsl:function>
<xsl:template match="outer">
<xsl:copy>
<xsl:sequence select="mf:group(record/taxNodes/node)"/>
</xsl:copy>
</xsl:template>
<xsl:template match="record">
<xsl:copy>
<xsl:copy-of select="id"/>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
That gives the desired result I think for the input sample you have posted, I am not sure it will do for other inputs, mainly as I am not sure how variable the input can be, I think if I understand the spec 'there is only one each of the taxonomic levels "a", "b", and "c"' correctly then it should work fine.
As for having a huge input file and using XSLT 3.0 (with streaming?), I am not sure that a streaming solution is possible, due to the nature of the problem where we need to recursively group the whole set of input nodes.

Answer 2

This stylesheet provides a solution but does so using a function for looping.
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:local="http://www.local.com"
exclude-result-prefixes="xs local"
version="2.0">
<xsl:output method="xml" indent="yes"/>
<xsl:template match="/">
<xsl:variable name="maxTaxonomyDepth" select="max(//node[not(node)]/count(ancestor-or-self::node))" as="xs:integer"/>
<xsl:sequence select="local:getTaxNodesForDepth(outer, 1, $maxTaxonomyDepth, '')" />
</xsl:template>
<xsl:function name="local:getTaxNodesForDepth">
<xsl:param name="out" as="element()" />
<xsl:param name="curDepth" as="xs:integer" />
<xsl:param name="maxDepth" as="xs:integer" />
<xsl:param name="parentId" as="xs:string*" />
<xsl:for-each select="distinct-values($out/record/taxNodes//node[count(ancestor-or-self::node) = $curDepth]
[if ($curDepth > 1) then parent::node/id/normalize-space(.) = $parentId else true()]
/id/normalize-space(.))">
<xsl:variable name="context" select="." as="xs:string" />
<node>
<xsl:sequence select="($out/record/taxNodes//node[count(ancestor-or-self::node) = $curDepth][id/normalize-space(.) = $context])[1]/(id | descriptor)" />
<xsl:apply-templates select="$out/record[taxNodes/descendant::node[last()][id/normalize-space(.) = $context]]" />
<xsl:choose>
<xsl:when test="$curDepth < $maxDepth">
<xsl:sequence select="local:getTaxNodesForDepth($out, $curDepth + 1, $maxDepth,
($out/record/taxNodes//node[count(ancestor-or-self::node) = $curDepth][id/normalize-space(.) = $context])[1]/id/normalize-space(.))" />
</xsl:when>
</xsl:choose>
</node>
</xsl:for-each>
</xsl:function>
<xsl:template match="taxNodes"/>
<xsl:template match="#*|node()" mode="#default">
<xsl:copy>
<xsl:apply-templates select="#*" mode="#current"/>
<xsl:apply-templates select="node()" mode="#current"/>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>