I found this intriguing... and not exactly clear (to me at least).
Test input
<?xml version="1.0" encoding="UTF-8"?>
<categories>
<item>
<artist>Sbout the Moon</artist>
<title>Carved in Stigmata Wounds</title>
</item>
<item>
<artist>Satyricon</artist>
<title>Rebel Extravaganza</title>
</item>
<item>
<artist>Secrets of the Moon</artist>
<title>Carved in Stigmata Wounds</title>
</item>
</categories>
That's not particularly useful input since all the artists begin with the
same letter, so go in the same group.
stylesheet:
<xsl:template match="/">
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="group"/>
I see no <group> elements in your data...
<xsl:template match="categories">
<xsl:for-each-group select="item" group-by="f:grouping-key(.)">
<xsl:value-of select="substring(artist,1,1)"/>
</xsl:for-each-group>
<xsl:apply-templates select="item"/>
</xsl:template>
Having created the groups, you're not doing much with them! I would expect
to see something like:
<xsl:template match="categories">
<xsl:for-each-group select="item" group-by="f:grouping-key(.)">
<page>
<title><xsl:value-of select="substring(artist,1,1)"/></title>
<xsl:apply-templates select="current-group()"/>
</page>
</xsl:for-each-group>
</xsl:template>
The apply-templates outside the for-each-group is particulary weird. Why
group the items and then display them ungrouped?
<xsl:template match="item">
<xsl:message>
<xsl:value-of select="f:grouping-key(.)[1]"/>
</xsl:message>
</xsl:template>
This gives the error
Error at function f:grouping-key() on line 28 of file:/c:/temp/test.xsl:
An empty sequence is not allowed as the result of function
f:grouping-key()
That's because my code was wrong (type checking is good at catching errors).
If the artist begins with "A", as all yours do, then it doesn't match any of
the ranges. I leave fixing that as an exercise to the reader: I was only
trying to sketch the idea.
(The idea of course is that all the artists whose names are in the range A-G
get the grouping key A, all those in the range H-L get the grouping key H,
and so on. If you want to display the grouping key as a page title, it would
probably be better to compute the grouping key not as "H" but as "H to L",
say. I did a similar exercise recently where we were grouping on numeric
bands, e.g. "from 1 to 10,000", "from 10,001 to 50,000" - it's the only case
I've seen where we wanted to sort the groups on anything other than the
grouping key.).
Michael Kay
http://www.saxonica.com/
<xsl:function name="f:grouping-key" as="xs:string">
<xsl:param name="item" as="element(item)"/>
<xsl:variable name="ranges">
<range from="A" to="G"/>
<range from="H" to="L"/>
<range from="M" to= "P"/>
<range from="Q" to= "Z"/>
</xsl:variable>
<xsl:sequence select="$ranges/range
[string(@from) lt substring($item/artist,1,1) and
string(@to) ge substring($item/artist,1,1)]/@from"/>
</xsl:function>
Comments:
1. If the item/artist are not lexically sequential it bombs.
2. I don't understand the grouping, hence the item template,
which shows outptu I don't understand either.
Anyone care to explain further please?
TIA daveP.
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