I would normally use maps for grouping in XPath 3.1. Ignoring the problem of
composite keys
map:merge(//row ! map:entry( key, .),
map{"duplicates":"combine"})
If the grouping key is composite, as in this example, then you can either form
a key by string concatenation, or use a multi-level map.
Michael Kay
Saxonica
On 30 May 2019, at 14:06, Martin Honnen martin(_dot_)honnen(_at_)gmx(_dot_)de
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
On 30.05.2019 14:46, Costello, Roger L. costello(_at_)mitre(_dot_)org wrote:
Hello XSLT/XPath experts!
My XML document consists of a series of rows.
Each row is identified by the combination of two child elements: ARPT__IDENT
and TRM__IDENT.
I want to group the rows. A group consists of those rows with the same
ARPT__IDENT and TRM__IDENT.
This XML document:
<Test>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>X</TRM__IDENT>
<Data>Foo</Data>
</row>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>X</TRM__IDENT>
<Data>Bar</Data>
</row>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>Y</TRM__IDENT>
<Data>Blah</Data>
</row>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>Y</TRM__IDENT>
<Data>Plugh</Data>
</row>
</Test>
is to be grouped this way:
<results>
<group>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>X</TRM__IDENT>
<Data>Foo</Data>
</row>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>X</TRM__IDENT>
<Data>Bar</Data>
</row>
</group>
<group>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>Y</TRM__IDENT>
<Data>Blah</Data>
</row>
<row>
<ARPT__IDENT>A</ARPT__IDENT>
<TRM__IDENT>Y</TRM__IDENT>
<Data>Plugh</Data>
</row>
</group>
</results>
I can use xsl:for-each-group to perform the grouping:
<xsl:template match="Test">
<xsl:variable name="rows" select="row" as="element(row)*"/>
<results>
<xsl:for-each-group select="$rows" group-by="concat(ARPT__IDENT,
'|', TRM__IDENT)">
<group>
<xsl:sequence select="current-group()" />
</group>
</xsl:for-each-group>
</results>
</xsl:template>
However, I want to create a variable -- $groups -- which holds the groups
and then iterate over the variable:
<results>
<xsl:for-each select="$groups">
<group>
<xsl:sequence select="." />
</group>
</xsl:for-each>
</results>
What XPath expression will yield the desired value for $groups?
<xsl:variable name="groups" select="???" />
Is there an XPath 2.0 expression that can be used?
What kind of sequence type would you expect that XPath expression to
return? You can't build sequences of sequences to somehow wrap the items
belonging to a group.
So unless you could move to XPath 3.1 with maps and/or arrays I don't
see an XPath type constructed with pure XPath to hold groups. And of
course even there it would be easier and smarter to use XSLT to create
the map or the nested sequence/array or array/sequence structure than to
rely on pure XPath I think.
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