I'm trying to figure out how to use XSLT Streaming (to reduce memory usage) in a scenario that requires grouping (with an arbitrary number of groups) and summing the group. So far I haven't been able to find any examples. Here's an example XML
<?xml version='1.0' encoding='UTF-8'?>
<Data>
<Entry>
<Genre>Fantasy</Genre>
<Condition>New</Condition>
<Format>Hardback</Format>
<Title>Birds</Title>
<Count>3</Count>
</Entry>
<Entry>
<Genre>Fantasy</Genre>
<Condition>New</Condition>
<Format>Hardback</Format>
<Title>Cats</Title>
<Count>2</Count>
</Entry>
<Entry>
<Genre>Non-Fiction</Genre>
<Condition>New</Condition>
<Format>Paperback</Format>
<Title>Dogs</Title>
<Count>4</Count>
</Entry>
</Data>
In XSLT 2.0 I would use this to group by Genre, Condition and Format and Sum the counts.
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" indent="yes" />
<xsl:template match="/">
<xsl:call-template name="body"/>
</xsl:template>
<xsl:template name="body">
<xsl:for-each-group select="Data/Entry" group-by="concat(Genre,Condition,Format)">
<xsl:value-of select="Genre"/>
<xsl:value-of select="Condition"/>
<xsl:value-of select="Format"/>
<xsl:value-of select="sum(current-group()/Count)"/>
</xsl:for-each-group>
</xsl:template>
</xsl:stylesheet>
For output I would get two lines, a sum of 5 for Fantasy, New, Hardback and a sum of 4 for Non-Fiction, New, Paperback.
Obviously this won't work with Streaming because the sum accesses the whole group. I think I need to iterate through the document twice. The first time I could build a map of the groups (creating a new group if one doesn't exist yet). The second time The problem is I also need an accumulator for each group with a rule that matches the group, and it doesn't seem you can create dynamic accumulators.
Is there a way to create accumulators on the fly? Is there another/easier way to do this with Streaming?