This code passes Saxon's streamability tests:
<xsl:stylesheet version="3.0" xmlns:xs="http://www.w3.org/2001/XMLSchema";
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>
<xsl:mode streamable="yes"/>
<xsl:template match="/">
<out>
<xsl:fork>
<xsl:for-each-group select="/*/row" group-by="((@* => copy-of() =>
sort((), function($x){name($x)})) ! (name() || '=' || string(.))) =>
string-join(' ')">
<xsl:sequence select="current-group()"/>
</xsl:for-each-group>
</xsl:fork>
</out>
</xsl:template>
</xsl:stylesheet>
Note that the sort() function requires XPath 3.1 so its streamability analysis
isn't covered in the XSLT 3.0 spec, but Saxon applies similar rules to
functions such as fn:filter: if the first argument is grounded then the
function is streamable.
The key here is the use of copy-of() to copy the attributes before sorting;
this enables the compiler to know that the sort function isn't going to do any
non-streamable navigation starting at the attribute node. In fact, after
sorting you could equally well call a user-defined function that sorts using
xsl:perform-sort.
Michael Kay
Saxonica
On 25 Sep 2019, at 22:44, Geert Bormans
geert(_at_)gbormans(_dot_)telenet(_dot_)be
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
All,
I a streaming XSLT 3.0, I have to group a series of elements by their
attribute names and values
I have issues making the group-by motionless
In a simplified example
<rows>
<row a="val-a-1" b="b-val"/>
<row a="val-a-2" b="b-val"/>
<row a="val-a-1" b="b-val"/>
<row a="val-a-2"/>
</rows>
I need grouping this way
<rowgroups>
<rowgroup hash="|a=val-a-1|b=b-val"/>
<rowgroup hash="|a=val-a-2|b=b-val"/>
<rowgroup hash="|a=val-a-2"/>
</rowgroups>
easily achieved this way
<xsl:fork>
<xsl:for-each-group select="*"
group-by="string-join(@*/concat('|', name(), '=', .), '')">
<rowgroup hash="{current-grouping-key()}"/>
</xsl:for-each-group>
</xsl:fork>
but, I could have data like this (third line attribute order swapped)
<rows>
<row a="val-a-1" b="b-val"/>
<row a="val-a-2" b="b-val"/>
<row b="b-val" a="val-a-1"/>
<row a="val-a-2"/>
</rows>
and this basically gives me a fourth group using the code above
So I want to make sure that the attributes order can be controlled when I
prepare the group-by, but any sorting attempt I make, leads to the group-by
no longer being motionless
I would welcome your suggestions
Thanks
Met vriendelijke groeten,
Best regards,
Geert Bormans
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