Combining entries to page numbers - xslt

Question

I have entries for an index such as the following:
<entry name="a" page="1" />
<entry name="b" page="3" />
<entry name="b" page="4" />
<entry name="b" page="6" />
<entry name="c" page="7" />
now I'd like to get something like
<index name="a" pages="1 />
<index name="b" pages="3-4, 6" />
<index name="c" pages="7" />
Is there some ready to use function for that?
I was thinking of a two pass solution, first put the index entries in a format such as
<index name="a" pages="1 />
<index name="b" pages="3 4 6" />
<index name="c" pages="7" />
and then turn "3 4 6" into "3-4, 6". The first step is easy:
<xsl:for-each-group select="index" group-adjacent="#name">
<xsl:element name="index">
<xsl:attribute name="name" select="#name"/>
<xsl:attribute name="pages" select="current-group()/#page"/>
</xsl:element>
</xsl:for-each-group>
(the attribute 'pages' here could be something different, of course)
Now comes the difficult step, how should I iterate through the list? There must be some clever solution as to check if the next following sibling/#page (I could put the pages into a sequence) is the current #page + 1.

Answer 1

Here is a sample:
<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:strip-space elements="*"/>
<xsl:output indent="yes"/>
<xsl:template match="entries">
<xsl:for-each-group select="entry" group-by="#name">
<index name="{current-grouping-key()}">
<xsl:attribute name="pages">
<xsl:for-each-group select="current-group()/xs:integer(#page)" group-by="position() - .">
<xsl:if test="position() gt 1">
<xsl:text>, </xsl:text>
</xsl:if>
<xsl:value-of select="if (current-group()[2])
then (current-group()[1], current-group()[last()])
else ."
separator="-"/>
</xsl:for-each-group>
</xsl:attribute>
</index>
</xsl:for-each-group>
</xsl:template>
</xsl:stylesheet>
With the input being
<entries>
<entry name="a" page="1" />
<entry name="b" page="3" />
<entry name="b" page="4" />
<entry name="b" page="6" />
<entry name="c" page="7" />
</entries>
I get the result
<index name="a" pages="1"/>
<index name="b" pages="3-4, 6"/>
<index name="c" pages="7"/>

Answer 2

Here is another solution:
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="xs" >
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="entries">
<xsl:for-each-group select="entry" group-by="#name">
<index name="{current-grouping-key()}">
<xsl:attribute name="pages">
<xsl:variable name="vAtribVals" as="xs:integer*">
<xsl:perform-sort select="current-group()/#page/xs:integer(.)">
<xsl:sort data-type="number"/>
</xsl:perform-sort>
</xsl:variable>
<xsl:sequence select=
"$vAtribVals[1],
for $k in 2 to count($vAtribVals)
return
if($vAtribVals[$k] - $vAtribVals[$k -1] ne 1)
then concat(',', $vAtribVals[$k])
else
if($vAtribVals[$k+1] - $vAtribVals[$k] ne 1)
then concat('-', $vAtribVals[$k])
else()
"/>
</xsl:attribute>
</index>
</xsl:for-each-group>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the following XML document:
<entries>
<entry name="a" page="1" />
<entry name="b" page="3" />
<entry name="b" page="4" />
<entry name="b" page="6" />
<entry name="c" page="7" />
</entries>
the wanted, correct result is produced:
<index name="a" pages="1"/>
<index name="b" pages="3-4,6"/>
<index name="c" pages="7"/>
Do note:
Thepage attributes are sorted before further processing, and this allows correct processing even if the entry elements do not occur in sorted order in the source XML document.
The processing doesn't depend on relationship between integer value and position, which makes it applicable in other cases, where the attribute values aren't integers.